The instructions are actually pretty clear if you've ever spent much time in a US city. The best advice I can give you is use your Rand-McNally.
Exit 52 will be clearly marked on signs, and you will find that you can prepare for an exit by just watching exit signs; they will count down or up as you approach it (eg exit 49, then 50, etc). Exit numbers are also marked clearly on your Rand McNally city map.
Most exits are left side, but right side exits are not unheard of. Again, this should be clear from highway signs, so assume left exit without any indication to the contrary.
If you do miss an exit, things can get a little crazy. Generally, wait till you see one with a highway overpass (don't panic, it's only gas and time), and you should be able to take that and turn around. Stay on your highway number if it splits (ie stay on I-90). Make sure the exit number doesn't change when travelling from the other direction to get back to your destination. Don't assume the Interstate is identical on both sides of the highway (ie eastbound 1-90 may not be westbound 1-90 on the other side when you turn around, but whatever it is will be clearly marked on the map.
It wouldn't hurt to get the map directions from Apple for westbound in case you have to turn around after missing an exit.
Mark your path with a highlighter on the Rand McNally or even better, on a city map you can buy at a service station sometime before Buffalo proper.
A competant co-pilot is extremely handy; by calling out exit numbers as you get close you can prepare your exit without having to actually watch anything but the road ahead and traffic around.
You probably can't miss I-90; it may well be the only highway you travel on after QEW. You can tell it's an Interstate because of the shape of the marker on your map (a 3-hump shield). Don't panic if I-90 (as indicated on your map) turns into or is called I-190 or some similar 3-digit Interstate.
1 or 2 digit Interstates:
Even last number Interstates: (eg I-94) East-West x-country
Odd last number Interstates: (eg I-35) North-South x-country
3 digit Interstates:
Even first number (eg I-494): Connects to another Interstate at each end. Usually goes around a city (more or less).
Odd first number (eg I-394) Connects to another Interstate at one end. Usually goes downtown.
Exit numbers: usually identified by a and b for East and West; ie 52a. Check your map to see which corresponds to your route, and take that.
From the look of your map, you will take I-190 East off the QEW. It should also claim to be an exit for I-90, even though technically you won't be on I-90 just yet.
If there's no East (from the look of the map, it might be called South) then take the one that claims to go to I-90; because the end of I-190 you don't want goes back to Canada, while the one you do want will meet I-90.
It also appears you will have to take pay attention when I-190 actually meets I-90. You want to go on I-90 East, so take the appropriate Exit or remain on the same road, depending on what the signs tell you to do.
From I-190 to I-90
From I-90 to AppleStore