Can someone help me solve a knitting question about making a baby blanket?

I taught myself some basic knitting skills awhile ago from a very good book. I never got all the way through the book although I do still have it. I’m able to knit small squares in lots of different patterns.

What I want to do is knit a baby blanket. I’ve confused myself though about how that is possible. The needle is only so big so how do I make a blanket big enough? Would I need to join two or more pieces together?

If you could explain to me how it works in basic language I’d greatly appreciate it. If you need more clarification about what I’m asking please ask. Thank You.