triangles or squares

Hello. this is my very first project, and im close to done. however, i have ran into some challanges due to the use of squares while modeling, and i have seen more profesional work later where they use triangles for the most.

i started this for a few months ago and i had noone teaching me, or learning me anything, so if any of you have some tips and tricks, it would be great, but my main question is, triangles or squares? is there any advantages or disadvantages with either of them? and is one better than the other at spesific things? im talking about character only now.

also feel free to give me other tips and tricks. again first project, barely any tutorials. so im kinda just using what i know.