Hello. I am looking for a bit of help, mainly from people with expertise in Doom, to begin speedrunning.

Also, my main goal is to get maybe a top 50 Knee-Deep in the Dead speedrun on Ultra Violence.

Welcome. You can look for help and guides in the game forums or discord server: https://www.speedrun.com/d2016/forum You will find the game experts there, not on the general forums.

(If you meant another Doom game, go to the relevant game in the Doom series: https://www.speedrun.com/doom )