One of the challenges of FCP is that it is different enough in its approach to editing that trying to walk through the same steps is not the solution. It’s about identifying the goal and then the path to that goal.
It looks like your initial question is about performing a 3-point edit (“do a mark in / mark out and then insert / overwrite edit”). That is doable in FCP, but because it is clip-focused rather than track-focused the steps are different.
I think the biggest challenge in grokking FCP is that thinks about clips’ relationships to each other rather than to absolute time and how that reshapes the approach to editing. Tracks are pretty essential for working in relation to time, but less so when the relationship dynamic changes.