finances and budgeting!

Ha
Ok so my boyfriend and I had been together for 7 years. We now have a 9 month old daughter and we really need to figure out some kind of budget to help us save! We literally live paycheck to paycheck and I'm not amazing with numbers, but I'm pretty good with my money..he's not really though. 
Anyone have tips on how we can figure this out?! We had to stop renting our 2 bedroom apartment and rent a single room from my grandma until we can figure out our finances and we are going crazy living with her!