How to enable auto capitals

how can i enable auto capitals for my emails ?

There is no TB option to do this. I don’t know if any operating system on which TB runs can do it (on mobiles, it is the OS or the keyboard/input app that usually does it) but I don’t think so.
There were addons that did it but the last one ceased to be updated in TB52:

If you can find something similar for Firefox, you can ask the author to port it to Thunderbird as the API is mostly the same.
Especially now when scripts can be injected into “Compose window” as well, it will be for sure possible to build one.

I got an AutoUp hack working in Thunderbird 78.

More info

it won’t let me add, a mesage comes up saying " it appears to be corrupt "

You don’t use the AutuUp addon itself. You use the userChrome.js addon with code which came from AutoUp.
It’s explained in the mozillazine link.

sorry dave i do appriceate your help, i just cant get it to work, do you have a download i can use that i can load directly in to tb

Nope. It’s not packaged like that. You have to install the userChrome.js addon and also create a file in your TB profile, as described by morat: