GUIminer is very old software
no1 it supports only GPU and CPU which even the cheapest ASIC on the market will beat the pants off the highest end GPU
no2 GUIminer last i checked only supports getwork which was abandoned in about 2014 and replaced with stratum and no pools i know of support getwork anymore, so youd have to run a getwork-stratum proxy ontop of guiminer to get it to work.
if you really want to just try bitcoin mining then use
https://bitminter.com/ as i said GPU and CPU mining is that pointless its less than worthless. you can get 5 year contracts for $1 that will beat even GTX1080ti's