Just download Half-Life 2 from Steam or you can download Source Unpack from Resources (Don't use it, if you're going to do RLD skip) To submit run you only need a video
press the button next to "Game Time and Auto Splitting are available (by fatalis)" that says "Activate" to get the auto splitter. For cut scene skips, there are a variety. I'd recommend watching waezone's tutorials, he has 2 live tutorials
and he is currently making a more up to date tutorial series https://www.youtube.com/playlist?list=PL84A17W6AtxVTZ7aErwsj94UOjwqqj_m-
these should give you most of the information you need, and the rest of his channel has some in depth tutorials on Red letter day skip, breenblast yesclip, and more.
It has recently been discovered that the commonly used speedrun package referred to as the "5135 Unpack" has made changes that grant its users unfair advantages which were never present in any vanilla version of the game.
In light of this discovery, We've released an update which fixes these is