Blocking question?

Can someone please explained what I need to block something, I’m pretty new to knitting so I have ALOT to learn still. Should you block all sweaters or everything you knit?

Not absolutely everything needs to be blocked. There’s an article about it here that covers the basics.

Blocking does make a difference in the appearance of many fibers, natural ones especially. I don’t generally block acrylic or blends myself, though sometimes if they’re curling it makes it easier to seam.