I built my first PC at 14 ( I'm 27 now ) so it's not as hard as you may think it is.
Research on what you are looking for ( or as people suggested; place your budgets/requirements here ) and then use http://pcpartpicker.com/ to " build " the pc.
It will tell you if anything is incompatible; and people here are definitely willing to help you fine tune your build and make it the best price for value.
Additionally; if you are " worried " about building the PC, just get all the parts and either ask your bro to do it and offer to buy him a beer or dinner or something; or go to your local small computer shop and they'll build it for you for $60 or so.
When I worked at a PC repair shop some people asked if they could come in on a slower day (typically mid week) to see how it's built.
If you can get that option from your bro or the PC store owner; I'd suggest taking advantage of it.
it's easy enough to build watching videos; but it's a more engaging experience if you watch someone build it next to you. ( and they can answer any questions you have ) --- Until you can stop death herself, I will ignore you like I would the ants beneath my feet