Okay check the box the motherboard came in or ask a family member if they did anything with the jumper cap. If you can't locate your jumper cap you can always buy a new one. (it's a shame they only come in bulk orders) but here you go:
https://www.amazon.com/uxcell®-2-54mm-Standard-Circuit-Shunts/dp/B00HR8DGZO/ref=sr_1_5?ie=UTF8&qid=1528678236&sr=8-5&keywords=jumper+cap
I recommend having the family member who helped you build it present before proceeding. Remember to do this while the computer is off and not plugged into an outlet
1. Turn off your computer.
2. Unplug the power cable from the PSU so that it is not plugged into the wall
3. Hold the power button for 5 seconds while the computer is not plugged in
4. Open the side panel of your case so you can see the motherboard.
5. Next to your graphics card are two small pins with a little cap approximatley located here:
6. Remove the cap on those 2 small pins
7. Place your jumper cap on the two small pins.
8. Count to 10
9. Remove your jumper cap from the 2 small pins
10. Place the other cap back on the 2 small pins (your jumper cap should no longer be on the motherboard, this is very important jumper caps are only used while the power is off then you need to remove it)
11. Plug your computer back into the wall
12. Turn on your computer
13. Enter the bios and see if the problem is resolved.
Here is the manual page for clearing cmos on your motherboard for reference:
If you have any questions let me know. Afterwards lets see if we can then disable the integrated graphics and make terraria run at full performance.