This is going to be relatively quick and not that in-depth as I myself have trouble explaining this myself, so I think its best to research thoughtforms yourself.
Thoughtforms are normally sentient-thoughts such as tulpas, etc, normally these do actually have a energetic body and such, or independent.
But they can be created so they infact do, and do not rely on you to live.
Another form of thoughtform is a non-sentient thought form that is made to do something, normally I use this in constructs and such to operate a part that a energetic part can not operate that easily, such as mind-construct interactions and such.
These are normally referred to be “Servitors”, but I refer to them as being “Thought-Based Constructs” as the name fits a lot more from my observations.
These can be made to be present in your mindscape or also known as your soul landscape. It is common to use a thought form to guard your mind and stop foreign thoughts from entering and such. But be warned, even thought forms can be damaged and “killed”.
As I said, that's all I will go into it for now, best to research up on another sites, such as Tulpamancy, etc.