Yes, hello!
As I understand it, helping people like you is exactly what this podcast was meant for in the first place.
Hm...how to boil down dice rolling...
[Note, I think I wrote this at the same time Jon wrote his answer, which I just saw pop up in my browser. You might already understand things like percentiles, but if not maybe you could use this as an outline of how to explain Call of Cthulhu dice to players who have never played an RPG. In either case, excuse the overlap!]
DICE
1. When a player wants their character to do something difficult or dramatic, figure out which of the skills on their sheet would be most appropriate, and ask them to roll two 10-sided dice. These are called "percentile dice," because they randomly generate a result from 1 to 100.**
2. If the number they roll is equal to or lower than the skill number on their sheet, they succeed. If not, they fail. In either case, you as the Keeper will probably have to figure out what success or failure really means.
Ex: The character goes to a newspaper office to see if there are any past articles about a spooky house. You ask them to roll a skill check against their "Library Use" skill. If they roll a number (say 10) that's lower than their skill level (say 40), you have to decide what information they find, if anything. Those kinds of things are usually outlined in the scenario notes, but sometimes they aren't. If the player fails the roll, you might tell them that they find nothing, or that they only found part of the information, or that the articles were taken out of the office by the original reporter, or a shady character -- etc. Just be aware that things get complicated when you introduce new information.
If the player is trying to do something that doesn't seem to have a relevant skill on the character sheet, you can usually multiply one of the attributes by five and come up with a plausible number. While there's a "jump" skill, and a "climb" skill, there isn't a "swing on chandelier" skill, so you could ask for a "DEX x 5" check to see if they succeed. A DEX of 11 would mean a 55, etc.
Those are the very bare-bones basics of the whole dice system. Honestly, you could easily run a non-combat game with only that much understanding of the rules, and have a great time. Adding combat adds only slightly more complication, like initiative order and damage ranges. There are also rules for adding qualities of success and failure to the dice results that add a lot of drama and fun.
[I'm leaving out my explanation of 1/5th and 1/2 rolls, because Jon said it better. I would add that a roll of 100 is considered to be a "fumble," and it means extra bad things happen, like a gun jams or a sneaking investigator wakes up a watchdog. Note that when you listen to Actual Plays, you'll hear many Keepers consider a result of 96-100 to be a "fumble," though it's not in the most recent rules that way. Fumbles are fun. I think all of us at MUP would recommend going by the 96-100 rule.]
**Just in case you weren't sure: One of the dice is the "tens" place, and the other is the "ones" place. You should decide which one is which before rolling. Often nowadays one of the 10-sided dice in a set will have two numbers on it, like 80, 40, 00 etc. That's the tens place. If not, you can just declare which one is "tens" (veterans will sometimes say "controls"), and which is the "ones." In my groups, we usually said that whichever of the two dice is darker in color was the "tens" place by default. By the way, a "0 + 0" (or a 00 + 0 ) is considered to be a 100, not zero. Therefore, it's the worst possible result you can get on a skill check.
RULES TO FOCUS ON
You'll also want to make sure you understand the Sanity mechanics. They work on the percentile system as well -- when a character sees something disturbing, they roll percentile dice. If the result is equal or lower than their current sanity, then they lose minimal or no points at all. If they fail, they lose the larger amount. The result is subtracted from their current sanity, so it becomes harder and harder to succeed. In published scenarios, this is usually expressed like "1/1d6+1." If you have to improvise a SAN check for something that's not in the scenario, there are some good guidelines for this on page 76 of the 6E rulebook.
You should also be totally confident about when to declare a character truly dead. Review the death and healing rules on page 54 in your 6E book. Make a cheat sheet for yourself if you need to. It's not that the death rules are hard to understand, it's just that a character death is a dramatic moment and the last thing you want to do is consult the rulebook when a PC's life hangs in the balance. A tip: when the character is declared dead, let them have a moment in the spotlight as they describe their last words or actions. This makes death a lot more fun, and helps players contribute to the horror.
MAINTAINING HORROR
This is a huge and subjective subject, but here are the tips that spring to my mind:
1. A little description goes a long way. Pick out a few details in a scene that will help players see and feel and smell the creepiest parts of your setting. No need to go on and on, but a few choice words can help a lot.
2. Unknowns are scarier than knowns. Focus on building atmosphere with secondary evidence rather than direct contact with the badness.
3. Let the players contribute to the horror. If you don't have buy-in, you don't have atmosphere. Ask leading questions that help the players imagine the circumstances. Spread the spotlight around.
4. Offer horrible choices. Should the investigators strike a deal with the badness? Should they tell their employer the whole truth? Should they suppress evidence to prevent panic and maintain appearances? Should they sacrifice something terrible to stanch something even more terrible? Investigator X sure is acting strange. Can she be trusted? Questions imply choice, so don't push too hard for a particular outcome.
5. Use music. It works. Find atmospheric tracks and play them at low volume during investigations. Play an ambient track of frogs during a scene at a swamp. Let me know if you need help with this. It involves mastering an iPod.
BEST STARTER SCENARIOS
Again, everyone will give you a different answer. If you have the 6E book and you don't want to shop around much, you can just run "The Haunting." I feel it has some pitfalls for new Keepers, but it's got a long tradition and a lot of people have made it work. If you don't mind making an extra purchase before game time, check out "Crack'd and Crook'd Manse" from
Mansions of Madness, or "The Reeling Midnight" or "Malice Everlasting" from
New Tales of the Miskatonic Valley.
Hope that helps. Please keep posting!