it's pretty easy to build a PC. Be sure to check youtube, lots of how to build computer videos including some fairly recent AMD Ryzen ones. The only thing you need to take care is to not bend the pins on the bottom of the AMD CPU when you are handling and installing it. The how to videos will show you the proper way to insert it. Everything else is straight forward and should be covered by the motherboard manual. The last thing after its up and running would be to download drivers, For Ryzen you really only need the Audio, Chipset and LAN drivers available here
https://www.gigabyte.com/us/Motherboard/B450M-DS3H-rev-10/support#support-dl-driver
You might also want to download AMD Ryzen Master software which is a greta monitoring and overclockign software
https://www.amd.com/en/technologies/ryzen-master
Few things to look for when build that can be easy to overlock
--Be sure the correct motherboard standoffs, the little risers that screw into the case to keep the mobo off the case are put in the correct spots for your mobo, they should line up with the holes in the mobo and then you screw the mobo mounting screws down into them
--Be sure to install your rear IO plate/shield. Also before you screw down your mobo make sure the port on the mobo and the holes in the plat are all lined up correctly.
--Dont over tighten, when screwing anything down typically with computers when the screw stops it means its out of threads and is as deep as it should go, too much pressure and you will over tighten down into the relatively cheap metal of the threads and potentially damage your components.
--Take your time, make sure everything is inserted and connected properly and I would suggest taking the time to run your power and other cables cleaning on the inside of your case, not only will it look nicer but it will help air flow.