so in ROTF after bumblbee is crying at the begining he uses the things on the side of his head to cover his eyes
are those supposed to be used for combat or maybe for transformation

you can see what i mean at about 1:22

 

Probably the equivelant of someone being able to wiggle their ears.

 

I thought, this thing needs to tears do not fall on the rest of the face, who knows what they are, perhaps, they are harmful to the metal.

 

Meh, probably not for anything particular or important. Just a little visual gag, which makes sense, given that they are advanced shape-shifting alien robots. Moving slab A and slab B over piece Z is the equivalent of frowning or - as Split Lip said - wiggling ones ears.

 

Yeah they can move their bodies in strange ways they're called Transformers so it makes sense that they can move almost all their body parts in in any direction. Maybe it is like wiggling their ears or something.

I mean how do you get Optimus Prime from a freaking semi-truck? With Transformer science that's how. Don't question it, you'll only hurt yourself.