Guide for - You have friends? - 15G - Complete 5 events online with other players
This is a pretty easy achievement to get depending on whether you have a friend or not to unlock this achievement with. Let me explain both solutions to get this achievement with less than an hours play for either method.
Online Solo Solution:
First off to get this you will have to select the Play Online option in the Menu. This game works off of a multiplayer free-roam lobby where everyone can select races and you can choose whether you want to play Solo or Challenge other players to an Online race before you start a race up, so it is up to you how you want to race and you will not have to unlock anything in the game before you can start to play online.
Once you are familiar with the game a little bit. You will notice that you spawn at the Garage in Palm City. Behind this area is a racetrack that has multiple Activities and Races. You will want to look for the Circuit Race called "The Resort's Circuit" this race takes a maximum of 2:00 minutes no matter which car you use to complete it and it is quite an easy race to drive around on. Once you've found it, select the "Challenge All" option and you will create a race event that will start with a 1 minute countdown. It will also show the number of players that have at least viewed the event while they've been driving around the map themselves. People can drop in and out freely at their own leisure during the countdown timer so if you see only 2-3 people when you first create it, you may find the next time you create a new race on it after not finding anyone that you'll be able to race eight people that have joined since then depending on who's joined since the event begun. Simply do this 5 times and you'll get the achievement. It all depends on who joins but from my experience most people that create a race will 8/10 times be racing on this track. If you see a message that the lobby for the game you are in is closing or you're not finding enough people in that race world then simply back out to the main screen and start up a new online session. You will eventually find a few people that will race it a few times at the very least.
(On a side note if you need cash for the game still to buy the parts you need, I would recommend going back to the garage after racing on it 1-2 times then going back in as the cash amount decreases everytime you race it before going back to the garage, you also do not need to finish first to get the full cash amount listed as the money you get from it is for just racing the event)
Online Party Solution:
For anyone with a friend or two that can complete this with them, you will be able to finish this particular achievement in less than half an hour of playtime. On the main menu, Create a Party for you and your friend(s) to join. Then the main host of the lobby should select to Play Online and you'll be able to play together. Once you're in the world head to the raceway mentioned above and find the race called "The Resort's Circuit" once you're there if you select the "Challenge Party" option you will be able to create a lobby for you and your friend(s) ONLY and once they have pressed Y to accept you can race AI and your friends until this is finished. Simply rinse and repeat until you've got your achievement.
(On a side note if you're both hovering over the race, the other players will not be able to accept the race as the game is presuming you may play it solo so it does not show it, simply reverse out of the area and you should still see it)
I hope this guide helped (it was probably a bit too in depth for what it's worth but anyone who wants to get an achievement quickly, this is probably the one for you if you have an hour spare)
If anyone can recommend something else to improve this solution, please leave a comment below and I will try and answer it or include it in this solution.
Good luck and Happy Hunting [: