Blender whole model is moving when just adjusting one bone

Hi I am 14 Years and work with blender for around 1 Year.
And I got a problem with a rig. i try to model and rig a crab. I already got some cool bones for the eyes eyebrows and eyelashes but now I am stucked ot the pliers of the crab. Everytime i try to parent the bones to my pliers It seems to work but when I try to pose it the whole object moves kinda wierd and not the part where the bone was for.
I already try to subdivide my plier in edit mode cause the main plane of the plier is just one mesh with no sundivisions but it also doesnt work.
There is also no bone stick out of my model
I use the blender version 2.9.

2020-12-07 20_49_03-Blender_ O__Blender_Kritsoffff_Kristofrigged.blend

Have you tried checking the weights of the bones? Seems like that could be the issue. Could you share the file here, we can download it and have a look.

Yes I checked the weight painting but i dont really understand what it does i always just hit automatic weights and then it usually works.
Here is the link I cant upload it on my Question because I am new to this page

Hi I just saw the file and yes its definitely a weight painting issue, but the problem is that We cant really paint weights that well because the sides of the hands dont have many vertices that we can work with.
What weight painting does is (automatic wights basically just automatically paints the weights for you) it assigns a weight between 0 to 1 (blue = 0, red = 1 in between are various shades and the color green which is around .5) when you move a bone it moves the geometrys vertices according to the weights painted (0 = no movement, or bone doesnt have an effect, .5 = half movement, bone only has half the influence, 1= fully controlled by the bone)
Sionce your model has very few vertices (as mentioned the sides of the claw dont have any vertices on the face, it only has bordering vertices)
Automatic weight assigned the best approximation which was .5 (around green) to all the faces for all the bones, hence all the bones influence the entire mesh to some degree.
Firstly you’ll need to make manual cuts in the mesh to add more geometry to the entire claw, and then manually paint in red the areas you want the bones to affect, and paint blue the areas you dont want the bones to affect
The following explains weight painting nicely.
The following is a great tip on weight painting with bones