Question about signature campaigns:
Do I just need to add the link to the campaign holder's site to my signature then change my profile picture to the campaign picture in order to receive payment for my posts?
You can trying to join signature campaign when you will become Junior Member (after reaching 30 activity). And you can set your avatar when you become Full Member (120 activity)
Try to search 'Signature Campaign' in service section and see what requirements are for some of them.
What do I do in the meantime?
In the meantime you can offer your services - but realistically you have to be good at something: programming, graphic designing - anything you can easily transfer via internet.
You can also look for various job offer in Service section: captcha solving, re-typing old WW2 documents, creating accounts or following people on social media for BTC etc.