Beginner jumping ahead.

Hello, I’m a beginner with 3D Modeling. I’m interested in modeling vehicles for games, specifically UT2004 or possible UT4 when vehicle game modes eventually arrive. I’m going through tutorials to learn the basics. I’ve imported tanks from UT2004 and UT3 as a reference. The block in the middle is the first steps in my attempt at making the basic shape for a tank body. It shows how much of a beginner I am.

I’ve decided that one way to learn is to modify existing models. I will, ofc, continue learning the basics from tutorials but it would be fun and motivational to try to add some detail to the UT2004 tank. I have some questions about that.

A lot of details on the UT2004 tank are implied by the image on the surface. I would like to change those implied details into real details, starting with the indentations on the rear fenders.

To get started I would like to create a poly on the surface and extrude it inwards. So far I have only done loop cuts and subdivides to create new edges so if anyone is patient enough to point me in the right direction I would appreciate it.

Can I apply a simply poly shape to a surface then extrude that shape? Can I freehand draw that shape? How would I lock that extrude to the local orientation of the surface?

Also, the model is all triangles (tessellated?). It seems to me that it would be easier at first to start extruding a shape from a single surface without crossing edges. Can I even extrude across multiple faces? How would I combine those two triangles around the selected line into one surface, assuming the two surfaces are in the same plane? I tried merging the faces but that didn’t work right.
I apologize for jumping ahead. Thanks for being patient with a beginner.

I will, ofc, continue learning the basics from tutorials
Maybe you should spend the 30 mins to start to learn the basic modelling tools before you start trying to model something.

Join selected adjacent faces with F or dissolve selected edges (X)

Try knife tools

I thought I made it very clear that I was jumping ahead of my knowledge. I have spent more than 30 minutes in tutorials and I hadn’t yet found the answers to my questions. After browsing the forums it seemed like a mature, patient, and helpful place that was friendly to beginners, yet the first reply to my first post is a rather snarky response from a moderator. Very discouraging.

Anyway, thank you for the information. That worked. As far as my other questions if anyone has the patient to answer them it would be much appreciated.