I think TC has had a recent upgrade, I turned it on this rvo and the grouping icons have coloured and a new one has popped up.
That tuning fork shaped thing takes you to another page where it's more like Fusion, where your can draw lines etc and bend the lines as you need, I used this for the indicator housings.
You'll get the hang of it pretty quick, of I'm modding a item, I double it out triple it before I start cutting and altering, yes you can reverse what's done but I have just deleted and gone with the spare to restart with. It's also handy to double it if you want to lengthen or widen by cutting the top off one and bottom off the other then join (union) together.
Thinkyverse and printables are my first point of search then I do a general search , I think printables is where I got the bulb holder file from and then integrated it to my indicator housing with TC. I have added to thinkyverse with a couple of things or modified someone else's. I did modify a solder wire holder to spool better and added a magnet slot so it can be stuck close to the wiring job, if it's a metal car etc.