How do I mow my grass?

My family just moved into a new house, but the old house barely had a lawn, with most of the backyard being gardens that out house-mate/landlord/friend took care of. We just got a new lawn mower for out house, but I dont really know how to mow the grass.

There's a front bit of grass by the curb with a tree in the way. How should I mow around it while keeping it looking nice?

There's a fenced in frontyard that has some rose bushes, and some sort of (dont know what kind yet) citrus tree. The grass is also very uneven here, the neibour's plastic thing idk what it is is peeling off their foundation and killing the grass, and I can't tell where the brick around the fence ends and the grass beguins. How do I get around these problems?

There's the backyard, which has a huge square porch and im not sure how to cut the grass on the edge of the porch. There (was) a fire pit which is now an anoying diagonal square in the corner that I cant really mow around or in the corner. Theres the edges which have plants hanging over the grass, and idk how to cut the grass there without damaging the plants. There's also 2 rock gardens next to the grass that keep putting rocks in the grass which are quite dangerous. How do I mow around all this?

I also just don't quite understand using the edge trimmer. I usually end up damaging the wire or cut more of the lawn than wanted.

I don't think I need to solve everything here, but It would certainly help to know what I'm doing and cause I don't really have much better to do this stuff has really been bugging me. Any ways to fix this stuff?