You need to understand the basics of the game to become a master. Here's the modes (obvious enough if you're a veteran)
FFA: Most begineers start here, not many pros are found here due to being boring. This mode will help you understand the game.
Teams: Intermediates and Begineers mixed. Due to not much players can eat you, this will allow you to understand some advanced tactics like shooting a virus against a player. More pros may appear.
Experimental: Advanced players usually play here due to the fact that the mode is harder than the first two. Players will discover red 240 mass viruses also known as Spawners. They can grow to the size of the map if fed mass. Pros are abundant here.
Party Mode: Not reccomended for beginners or intermediates. This mode is infested with Advanced and Pro players, mostly teamers. Unless if you are going to break your desktop, hang off the mode until you git gud. You will need to learn a lot of advanced tactics like destroying a team and virus-shooting, as those are essential in Party Mode. Never should a newbie go to this mode unless if they have learned from, let's say... Some pros. If you want to learn more, watch some youtubers. Jumbo and Wun Wun are already pros from the start. They are also team-killers.
Private Servers: The most fun mode to play. Only available when you host one. Nothing else to say.