How do I do these things...

[Ofnuts]

1) Try Filters > Distorts >Curve bend. But if it's the text layer see https://www.gimp-forum.net/Thread-ofn-bend-path

2)

1. create the text layer (because you don't know the size of the rest until you have done that)
   
2. add a white layer, crop it around the text (crop tool or selection+Select>Invert+[delete]
   
3. Filters>Light and Shadow>Drop shadow