Not sure how much you guys understood from yesterday's post but here's some more info. I was still a bit confused about the mechanics of GTA Online yesterday bu after today's 3-hour long session and chatting with some friends, I decided to do up another post.
Story missions are similar to the ones you find in GTA V. You meet NPCs like Lamar, Simeon and Gerald and instead of activating missions via driving over to them, you call them and request a mission, and the guy sends you a sms which goes into your job list. These "jobs" can be done alone or with friends.
You start up the job and the menu opens up to let you invite your friends/crew members in. Increase the difficulty for higher rewards like XP. These are generally for smaller parties. Once the job ends, you can go back to free-roam or play other missions.
While jobs can only be activated via your phone, another way to complete missions with your friends is via the pause menu. This opens up a playlist with death-matches, team-matches and races. You can either pick your own playlist or go into a voting system with the rest of the players.
You will also be able to start up these games by driving to the pointer in the map when in free-roam.
Free Roam (Some stuff that you can do via free-roam)
Rob Stores / Hold-Ups - These aren't exactly missions, anyone who knows what you are doing can rob a store with you. The one who takes the loot can share the cash with the rest.
Steal Cars - You can sell cars that you steal in LS Customs but this can only be done once per game day (around 50 mins or so). You will also not be able to sell high-end cars. I read online that you won't be able to even enter LS Customs with a high-end car that you stole. This probably also affects why you won't be able to steal a high-end car to keep as your own. So you will have to purchase those cars if you want them. I haven't actually tried these but it makes sense.
I was wondering why it would be possible to steal cars to keep when they are supposed to be purchased.
Buy Apartments / Garages - Yes, you can. Costs a lot but all that money you earn can be used to show off your wealth. I like this aspect in GTA Online. No point having millions when it's just a figure. For starters, you can get a free 2-car garage.
Bring up the phone and access the internet. Under the properties, you will see that one of the garages is free. Do note that you have to purchase it online. I drove down to the garage and tried to purchase it but it didn't allow me to as I would need $25k. Would be annoying if you did have the $25k and splurged it all on this small garage when you could have gotten it free. I read that this is only for Social Club members though. One of the perks for signing up for the free Social Club... What are you waiting for?
Car Customization - Like in GTA V, you can upgrade or customize your ride with cash. However, I brought a Bravado Buffalo (Franklin's Default car) to LS Customs but it didn't have all the customization options as GTA V. They weren't locked, they just weren't there. For example, the "Hood" options weren't available so not sure what's up with that. Still pretty cool though.. Can't wait to have a Garage full of Sports Cars!
I'm only level 10 now so there's still plenty of content left that I have yet to see or unlock. It's been fun playing with friends and crew members. While I have been lucky not to have been hit by any major glitches, there are some people who have lost their Online saves or cash earned. Just hoping Rockstar will solve everything asap as it will be a real pity for people to turn away from GTA Online when it has so so much potential. To think that this is just the beginning is mind-boggling. Rockstar also promised so much more content in the future including adding the entire GTA IV's Liberty City. That is just incredible!
Hope my posts have given a better idea to those who have just started on GTA Online and helps clear some of the questions you might have. I haven't checked out everything or gone online to find out everything as I really wanted to experience as much as possible first-hand.