Recently my manual 2001 ranger has stopped going into first gear. It will go into any other gear just as it always has just not first. It won’t go running or not. This is my first manual so and I don’t really too much about what it could be

 

Welcome to the forum

No obvious answer to that
1 and 2 used the same shift fork to move the "dog gear"/collar into its 2 positions, 1 or 2
Could be synchro gear on 1 is broken and blocking the shift to 1
Could be shift fork is worn so can't move it to 1st

Not much you can do to find the problem without pulling out the transmission and pulling off the top plate to look inside

You have an M5OD-R1 manual transmission, aka M5R1
These are engine specific transmissions, i.e. an M5R1 from a 3.0l won't fit on a 2.3l or 4.0l and visa versa, also 2WD or 4WD are specific, not interchangeable
M5R1 was used in Rangers/Mazda B-series from 1988 thru 2011

Very rare to have a problem with these transmissions which is why Ford used them for 24 years
But this also makes used ones a safe bet if you just want to swap transmissions

These M5R1 manual transmissions used ATF, yes, automatic transmission fluid in a manual trans, Mercon V
People(even shops) could use Gear Oil, like older manuals used, which could "kill" these transmissions