Also a good idea to kill the heat and let residual heat take it from there when you're melting stuff. At least, that's what I've found. Gentle heat is best, don't let it get to boiling.

[She shakes her head.]

Seizing up means the chocolate's become grainy and clumpy and... kinda gross-looking? It's what happens when moisture's introduced to it. I can go into the science behind it if you want, but the big takeaway here is make sure your utensils you use are dry too, and don't use anything that can retain moisture, like wooden spoons. Seized chocolate can be salvaged... if maybe having to be used for other stuff, burnt chocolate can't.