u/selfmadesoloin r/compsci • Recommends
On “in what ways are we able to know if a software would be fast or not?”
Foundation of time complexity is in Mathematics, so yes it's effective. It can turn from a beginner level topic to advanced. Time complexity is usually taught in the end of first year or in second year in most universities in a Computer Science program. But it can also be self taught there are tonnes of resources out there that will give brief understanding of it in about an hour and array of courses online that can help you learn it in depth.
This link to this video might help you a little bit if you are interested. But learning basics of time complexity is extremely important because any good Software engineer/developer position will require you to know that.