what car is it?
Anyway thats rot - on a bad level
The floor plan - that'll punch out with a screwdriver, find out where the rot stops and you find good metal
An angle grinder or even a dremel will do this to cut neat shapes
The Sill - thats a cut and weld up job as well - that looks like somebody jacked it up wrong....
Note - both are MOT failures
Ziggy