Loco, 1st and reverse are non-syncro gears. You have to be close to a full stop and wait a second for the input shaft to stop spinning after pushing in the clutch. Then you will get it to go into gear. 2nd-4th gears have syncro's that match the speed of the mating gears so they can mesh smoothly.
If you cant get it into 1st or reverse at all after stopping and waiting a few seconds then you may need to adjust your clutch linkage to be sure your clutch is fully disengaging.
