Your monitor choice largely dictates your parts and selections.
If you're trying to game on a 4k monitor, your needs are different than gaming on a 1080p tv.
From there, your quality requirements needs to be addressed. Are you looking for 100+Fps at ultra quality? Are you content with medium quality at 60fps?
Are you looking for basically a plug n play experience?
And after you decide all that, then we get to factor in budget.
If you're on a REALLY tight budget, and looking for "living room gaming", then a PC isn't your best choice. A console is more than likely the best route for you to take.
That said, if you're not keeping up with the tech, you are largely at the mercy of recommendations of others.
- In general, an i5 is always your best choice for gaming. Powerful enough for all games at any settings, cheaper than the i7 counterpart for minimal gains.
- buying the "best" hardware is typically a fools errand; more for the enthusiast than the average consumer. Everyone wants the best, but an i5 and a 1060 is quite a decent gaming machine @ 1080p.
The right motherboard is usually dicated by budget than any other means. You should get the best* motherboard you can get that fits in your budget ( to a point). Why? Upgrade path as well as reliability. Buying a 40$ B series motherboard will "work", but you are severely limited by I/O, overclocking capabilitries, upgrade paths, pcie, sata, etc. Buying a 400$ top of the line motherboard is also probably not the best choice for most persons. There is a point of diminishing returns around the 150$ mark with most motherboard markets. Looking for long term, reliable solution with overclocking headroom is typically what we suggest around here.
TL;DR
Step 1) do your research
Step 2) ask questions
Step 3) select parts
Step 4) confirm selections with more experienced persons***, and accept the feedback given. Sometimes people like to spend your money for you, so you also need to take recommendations with a grain of salt.
Step 5) repeat 1-4 until youre ready to make a purchase
*** be wary of where you get your advice. Reddit, linustechtips forum, youtube, etc are generally TERRIBLE places to get solid information. i.e. Me -> "No tim, you really dont need a 1200 watt psu any more" Tim -> "But EVGA says I need 500w per card..." Dave -> "Yeah man, he needs the 1200w for upgradeability. What if he wants to sli his gpu" *Sigh*...