Going from a pile of parts to a functioning AR isn’t very hard. There are countless youtube videos and guides on how to build AR15s. This isn’t a detailed guide, but a little commentary on the last upper I assembled.
I find installing the port cover annoying. I’ve done it enough times I can do it quickly, but it is still annoying.
The pin can start from the front or the rear of the receiver, but it tends to be easier to work from the front. Once started, get that spring in place.
Give the spring a wind and push the rod through.
Then watch it pop out of place and do it again.
Then drop the C clip in the carpet and wait till a new one arrives in the mail.
Then get that little annoying thing snapped in place.
The forward assist should be simple to install. Simply depress the forward assist and insert the roll pin. The notch on the forward assist will keep it captive.
You’ll note that I don’t have a photo of the installed forward assist as I managed to flair out the roll pin and had to get a replacement. 5/8th inch long, 3/32 diameter, and you can get a 100 pack from McMasterCarr for a few bucks.
Install the roll pin for the forward assist from the bottom of the receiver. That way if(when) you slip with a hammer and punch, you ding up the bottom of the upper which few people will ever see.
Fortunately barrel components slide together then screw on the upper and you get a working gun in no time.