I’m not sure what you are asking here but let me take a guess.
You can “edit or cut” layers using keyboard commands.
Unlike a NLE the footage in AE stacks, so a new bit of footage is farther down the time line and sits above other layers and it steps on the footage below.
If you put your time marker over a layer and hit cntl shift D that will split the layer at that point and put the second part above the first in the stack – so that’s like a cut.
You can just slide the elements in the timeline back and forth to line them up how you want with the top layer stepping on the lower layer when you want the new footage to take over. *holding shift will snap a layer to other layers end points)
There is no simple dissolve in AE like a NLE. You can do it but its messy. Let me know and I can walk you through it or you can look up the blend effect. Keyframing transparency can work but it’s hard to get the roll off from one to the next. But if you are just “disssolving” from a top layer to a bottom layer this can work fine – just keyframe the trani attribute of the top layer and let it fade in our fade out covering the bottom layer.
Trimming a layer is alt plus the right and left sqaure bracket keys (the trim will happen where your time marker is). You can bring the end of a clip to where you want it by hitting the sqaure bracket keys without the alt.
You can get to the begining of a clip by hitting the i key (for in) and the end by the o key (for out)
Keep in mind when you trim, you are sitting on the last frame of video not the next frame.
For a slide show of all the same length its really easy. Just bring in all the clips you want into one big stack in the time line. Make them all the same length for how long you want them to be on scren. Put them in the order you want to see them from top to bottom and then select all, the right click and choose Keyframe Assistant and choose sequence layers. Choose no overlap and bingo a staircase of shots cutting from one to the next.