Brief run-down of how things work, it's pretty general since a lot of things change from season to season (and players usually aren't told about it in advance).
We start out divided into tribes, usually two of them but sometimes more. Tribes compete in challenges for rewards and for immunity -- the actual game takes place on a deserted island, so rewards are things like food, blankets, tarps, stuff like that; the forum game has different types of rewards. Immunity challenges are where one tribe will "lose" the challenge and have to go to Tribal Council.
At Tribal Council, everyone in the tribe casts a vote for someone to boot (can't vote for yourself). The person with the most votes is eliminated from the game.
At some point, all the tribes will merge into one tribe; at this point, challenges become individual challenges (though some reward challenges will be played in teams, or the winner of the reward can pick some other people to share the reward with them). During the tribal phase, only the people on the losing tribe go to Tribal Council and vote, but after the merge, everyone votes, including the person with immunity. You just can't vote for the person with immunity. Still, most votes is eliminated.
At some point, eliminated players will no longer be completely out of the game, but instead they will join the jury -- they aren't eligible to win the game anymore, but they are the ones who will eventually determine the winner.
At some point, usually when there are 2 or 3 people left, we stop voting people out of the game, and instead have Final Tribal Council. This is where the jury addresses the finalists and will vote for a winner -- the most jury votes will win the game and become Sole Survivor.
Those are the rules, they are pretty simple: you can use whatever criteria you want for casting your votes (and your jury votes), but on the show people quickly realized that they need to form alliances with other people to get a majority of the votes on their tribe, otherwise they end up getting voted off. So a lot of the game takes place in QTs with various combinations of people in order to form alliances, but even if that alliance makes it all the way and votes everybody off, eventually they have to turn on each other because there can only be one winner.
There are many ways to play the game, and people have had success with all of them on the show: you can play a physical game and just try to win all of the challenges. You can play a strategic game and form lots of alliances to keep the votes off of you. You can play a social game and just befriend everyone so they don't want to vote you off.
In a forum setting, the challenges are a little different than on the show, but many people have said that the challenges are their favorite part of the game. You can check out
last season's OP for links to all of the challenges that were done last season.
Time commitment? Forum Survivor is a game that gives back what you put into it: if you want to, you can spend hours every day playing the game and have tons of fun doing it. If you don't have that kind of time, checking in once per day is plenty to do everything you need to do, and V/LA is pretty much always fine as long as the mod knows about it, especially early on in the game when you can just sit people out of challenges if necessary.
The last two seasons took about nine months from start to finish. Yeah that's a long time but most people didn't end up playing the game for that long, as people are eliminated throughout the game. In both seasons, we've had people who wanted to bow out because something came up and they didn't have the time, or it turns out they weren't having too much fun: that's totally OK and easy to deal with (as long as you are open about it with the mod).
I tried playing a forum game a long time ago and it wasn't really my thing, but I can't get enough of Forum Survivor. It's certainly a different experience, and in my mind it's a way better one. Hopefully you decide to give it a shot