1. CHECKING
first things first, you need to install a 1080ti. so please do check your case's size and the power connectors for 1080ti. if you have any other PCI card installed near the 1080 then it may block air. which will result high temperature and noise
and also the power supply needs to be strong to be able to run it. i do not trust anything below B (bronze) rated PSU.
PSU Wattage is not the thing you need to worry about because 750w is sufficient for running a 1080ti, but it must have a good rating especially when you are using such high-end GPU. PFC is another factor but it matters. i recommend you to read tom's hardware guide to install Graphic card. instead of searching on forums and waiting.
2. installing
Place the box on a anti-static surface or ground. keep it away from things which can generate static electricity like carpets, and clothes, even the hairs on your hand can cause the GPU to damage, so sit on ground or just wear a anti-static wrist band.
Slowly take the GPU out of the packaging and place it on the box.
Place your PC case on ground and then open it. remove case's Expansion slots next to the PCI-E slot.
Take the gpu and gently push it PCI-E slot, Make sure the port side is facing to the expansion slot. Push it again properly and make sure it's perfectly fitted in the PCI-E slot.
now screw the card on the expansion slot if you do not do it then the chances are that your card or the PCI-E slot will be ripped off. after screwing just connect the power cables and make sure they fitted.
Now screw the side of the case and put it back to your desk, start it and then just go to your manufacturer's website and download the 1080Ti drivers. and you are ready to play!
Thanks for reading, hope it helps (sorry for my bad English)