How do I Install/build front and side doors?

You may need to pull permit and comply to local building codes. Check with your village hall.

https://www.bhg.com/home-improvement/door/door-repair/how-to-frame-for-a-new-exterior-door/

https://www.do-it-yourself-help.com/framing_a_door.html

https://extremehowto.com/installing-a-new-exterior-door/

https://www.doityourself.com/stry/how-to-frame-an-exterior-door-opening-part-2

https://www.youtube.com/watch?v=Y6QitL-cerc

It looks easy to do but you need two people to do the job. Everything has to be perfectly level and you need to allow at least an inch around the door frame for insulation and a place to put the shims in to make the door even on all sides. If you have not done it before, then maybe you can obtain the help of someone who has. A good carpenter will put those in, in little time.

Unless you are comfortable with carpentry, please do not try to so this as the frame has to be level or the door will not hang properly.

Well I did this at my moms house, and it was not as easy as you might imagine and best done with two people. You must follow local Building code too. When I had to redo the door leading from my house to garage, I hired out. Not cheap, but worth it to me. If you have the skills and tools, go for it. If not, at least spring for a handyman to come and help. Just know you need it to be done right for optimal efficiency and the safety of your family. Watch a boatload of You Tube videos too.