Don’t even know where to begin

The clunk and dying isn’t a confidence builder…….

I’d go with the two easiest things first…….
Is there enough fluid in it?
If so, I’d back off the kickdown cable a bit.

Get the rear end on some jackstands.

Start out with the shifter pulled all the way into low gear……bring rpm up to around 2k or so, and select 2nd.
There should be a noticeable shift happening after the lever is moved.

If that doesn’t happen the next thing I’d do is verify the shift linkage is properly adjusted.

If it is, then you might have deeper problems.