Solo: You don't need a team to make a game in a jam. If you are not very good at art and music there you can just make pixel art and simple music. Game jams are a great way to improve your weaknesses so I would't be afraid about that. I've participated in several jams solo and it isn't a problem.

Teaming: Teaming up is another great option but you'll have to be in constant comunication with the team so if you're shy it can be a bit difficult, but there are a lot of great people there who would understand your situation (And this could be a chance to overcome your shiness).

My final advice would be: If you want to participate in a team, just do it, but do not be afraid to participate solo. The worst thing you can do is missing the jam because of indecision.

Here are some simple tools to make art and music:

Piskel: Webpage to make pixel art https://www.piskelapp.com/

Sfxr: Simpe and very easy program to generate sound effects http://www.drpetter.se/project_sfxr.html

Bosca Ceoil: A program to make game music  https://boscaceoil.net/ (Brackeys has a tutorial about this program) 

SOLO: absolutely solo, teaming up is a pain in the ass if you dont know the people directly, and contact them directly, like call, meetup...