from the one picture it gets hard to say why aand what.
As far as I can se, there is only one really fix part the "fuselage.par" which was obviously the first part in that assembly.
From there on all parts don't have a full constraint condition.
So without knowing which part You have selected at the moment, which connections or relations this part will have and will not have, there is no way to give the right answer.
Execpt, as long as there are moveable parts there on which You put a new part, all of them will be able to be moved.
just watched the vieo a second time and OK, now I've seen it is the DOOR.par You are talking about.
But this part seems do hasn't any relation so far.
Maybe the issue will be, that You only select a movement in one direction.
Take the global movement (right icon) and I suppose YOu will be able to move the door in any direction and any position.
And I'm absoluteley confident, that You will be able to define 3 relations and conditins to bring the door into the right position.
Worst way would be to use construction geometry or planes or coordinate system of both parts.
If the cylinder will be the saem for door and plane the You can use a sketch geometry for position it.
or - even easier and IMHO better - if the outer surface should be the same, then define a complete model of the outer surface from which You can split it into door and the rest
So the always stay associative and equal
Yes, if You click the linear movement in smart ribbon bar, then only a linear translation will be possible.
Take the 3rd one (general movement) and I suppose, a movement in all directions will be possible.
If I interprete Your video correctly, then no relations are defined for this part so far
I couldn't define any relation as I wanted so I used drag component command for all assemblies. I used move component now to move the door down. when I use mate command I can mate one edge but then I can't mate the other edge. it would be nice to use one mated edge as a hinge and move the door along it's axis.