Okay, so first of all: Welcome!

1. Driving on the public servers should not be a problem, since they do not use modded content and don't require a password. Maybe the server was full and you couldn't join because of that? Keep an eye on error messages in the bottom of the screen when you try to enter, sometimes they tell you about the problem. Sometimes the resolution changes in the game options, whenever I can't join, that's the first thing I check.

2. Donating is always very welcome, though not required to drive on the servers. After donating your download speed in the Autoupdater should drastically increase, even if nobody messaged you.

3. The Autoupdater: If you don't have it yet, download it from Downloads section in the top left. With it you download and install all new mods automatically, which you need for most event races and the servers 1-3.

I hope I could help, keep asking if you still have difficulties

Cheers,
Haggard