Looking to redo the plumbing under my kitchen sink

I am looking to finally start a project that I have been procrastinating with. I am looking for some assistance to determine how best to redo the plumbing under my kitchen sink. I have been advised to cut the pipe after the p-trap but I don't know how to begin to rebuild the piping given that I would like to add a clean out.

My brain does not understand how to cut the pipe between the 45 elbow and p-trap and then what do I do. I guess I am too much of a newbie. I don't think I would have much trouble if I could cut between the wall and the 45 elbow. Thanks.

If you are adding a cleanout, you can replace the 45 with a wye fitting, and stuff a cleanout fitting facing outwards.

By the way, the santee in this photo is upside down.

While you're at it, you should replace that section of exposed NM cable with a proper conduit, and also that nail-on
plastic box. That kind of stuff was never meant to be installed in exposed locations.

we would just cut between the 45 and the wall and then start putting the necessary pieces together.