Hello, Everyone, I just want to find out what factors make the CPU usage go up?

answer: fundamental arithmetical operations

there are two kinds of processors: RISC and CISC
RISC processors use a reduced, but faster executing set of instructions which means they do their work with simple arithmetic operations, whereas the C in CISC means complex. we´re talking about ~160 (RISC) ~260(CISC) basic instructions (please do correct this, for i roughly estimate these numbers).
Intel-based cpu´s are CISC-processors

That´s it-don´t be too shy to search on the terms "cpu architecture, publication(s), tanenbaum, ...). Especially linux related documentation really is detailed-much more transparent, though more "scientific" than the microsoft thing.
Reckon´ this will tell you a lot more, if you´re really interested in