I need to learn how to cut proper angles for trim around doors etc.

You can buy a box that has all your mitered angles cut in it. Start with your header pce ( top) measure from inside top corner of your door jam to the other inside side top corner add a extra 1/8 of a inch that will give you a 1/16 extra on each side reveal around your door. That is going to be your mitered cut measurement of the short ( bottom) of your 45 degree cut . Just 45 one end then flip your trim over measure from the short across your trim using the measurement you have got from inside jam cut at 45 again. Now tack the header in center so you can still adjust it later if you have tomake sure you are centered with corners leaving a 1/16 reveal from bottom of the top door jam. Now the sides measure each side separately cause they vary sometimes . Measure from the top outside corner of header to the floor. Cut your 45 now measure your trim from the long edge of the 45 down and do straight cut. Install that side. Flip trim upside down if using miter saw to do other side. Repeat steps above . Adjust header slightly up or down if you need to so you have tight joints and nail it all off. I hope this helps you out. Good luck.

Lots more videos if you click on the link.

https://www.youtube.com/watch?v=ZRYTr-SDSlY

Yes thank you so much

It's looks easy for an expert. I still haven't mastered trim cutting.

purchase a mitre box...all your angles will come out perfectly!

Invest in a mitre box and watch a bunch of utube videos. Practice makes perfect, you will get the hang of it!

YouTube has any number of videos: https://www.youtube.com/results?search_query=how+to+cut+trim+molding+angles+for+doors

There are all manner of videos on YOUTUBE dealing with miters.

HELLO,

You can buy Mitre Saw, That would help. Practice Practice Practice........