Is this normal in Manual transmission?

[Loren]

Yes, it's normal.

If you're patient, going slow enough (yes, you have to be going slow) and just keep gentle pressure on the lever, what's happening is that the synchros in the transmission are working to bring first gear up to the proper speed to slip in.

If you're less patient, try giving the throttle a little blip after you come out of 2nd, but before you try to go to first. That little blip will spin up the input shaft and if you do it right, it will help smooth the downshift. (it's called "rev-matching", Google it)

While the synchros WILL allow you to downshift to first while you're moving, more often than not, there's no need to do so and you're just causing extra wear on the transmission by doing it. Wait until you're stopped and it will slip right in.