Hi Sam and welcome to Sparkpeople!
I'm a "newbie" to SP, too, and have been using the site about 2 weeks now. I found it helpful to start out by logging what I eat/drink in the Nutrition tracker. You can also log your exercise in the fitness tracker. A feature that I find really helpful is to run a daily report on my nutrition which gives me tips on how I can improve my nutrition.
I learned my way around the site by working on Sparkpoints. If you click on my Sparkpoints in the tracker link, it will open a page with links to read articles, log goals, post messages, etc. You can also earn points while you complete these steps and then use these points to "buy" goodies for yourself as a reward and also give these as gifts to other SP members.
If you haven't had a chance, I'd recommend checking out the teams section and joining a few. This is a great way to meet people with similar interests. I've found the support from other SP members so helpful and motivating and hope you encounter the same.
Good luck in working towards your goals!!