I am debating internally how to answer this. The reason being that, despite what you might think, I am heavily invested in helping people learn to do new things, I spend quite a few hours every week answering questions from novice knifemakers helping them get started with their early projects, and I spend a lot of time on this forum doing what I can to pay back the help people here gave me when I was getting started with CNC. I really believe that this is important.
The issue is that building a DIY cnc machine is pretty much the ultimate exercise in self-directed learning. You are going to encounter difficult new topics to learn every few minutes, and some of the things you need to do to build a CNC machine (especially a laser) are going to involve working with things that are potentially very dangerous. High voltages, linear stages that could crush or amputate a finger or hand, laser beams, etc... Some of the decisions you will have to make involve potentially quite complicated math: how about determining the size of servo or stepper you need to drive an axis of a given size? Moment of inertia of your ballscrew/coupler/load assembly?
If you are not comfortable researching the very basic terms you were asking about above, then you are going to have a difficult time getting any level of progress without having someone else help you through the entire build. I googled the 3 terms you asked about above ('feedrate', 'stepover', 'assist gas') and got useful articles for all three terms as the first result each time.
The internet is an amazing place. Find the right forum (like this one or CNC Zone) and complete strangers will spend some of their valuable time helping you learn a new topic or skill. But part of that exchange involves being respectful of everyone's time. If someone uses a term that you don't understand the first thing to do is to attempt to research that term on your own, if that turns up nothing then another post requesting clarification is totally warranted, but to get people to help you you're going to have to demonstrate that you're doing what you can to help yourself first.
Respectfully,
Aaron