Hello and welcome!
Always good to see new people coming in and wanting to give the content creating a go
my first thing is, there may be terms and words said that might be a little confusing so I apologise if some words are a bit strange.
As you asked for tools, I will list a few things here, basically all the tools I use. This might definitely be throwing in the deep end and require a bit of searching in the tools and utilities subforum but:
Track Editor - I know that sounds trivial but it's necessary for importing/exporting LMap (Landmap) and HMap (Heightmap) as well as placing some crucial objects like checkpoints, AI line, pit crew, starting positions. To make up for it, here is an incredible tutorial by TuomoH with getting used to the editor that'll explain things better than I ever can
viewtopic.php?f=9&t=5448
GIMP - Photo editing tool to edit the LMap and some HMap's, things like the circuit layout, runoff. Extremely powerful for making the LMap easier to make.
https://www.gimp.org/
While I'm here, a member has some video tutorials on some techniques and while they're using Photoshop, I think it's still valuable for the mean time
https://www.youtube.com/watch?v=uXl8JQMC5mw
GRHME - GeneRally HMap Editor - Fantastic 3D visual editor that can be used to create HMap and get a good view of the track overall
viewtopic.php?f=8&t=733
SnakeDitor - You can actually use this to make layouts too. I use it primarily for object placement because it is wonderful for making objects lineup neatly and place and move them. There is an included document on how to use (this can be a little fiddly to use sometimes)
viewtopic.php?f=8&t=142
Here I was thinking I used more tools but the reality is, that's about all I use.
Hopefully it's enough to get you curious at least. I'm sure other users do things in different ways but feel free to experiment and explore