Objects distorting when rigging a character

I tried to make character Rigging and move them naturally, but the other parts keep distorting. The image of YouTube, which I originally tried to copy and practice, naturally moves the body, but what options or mistakes are causing this phenomenon?

(First image is mine, Second image is reference image for practicing.)

maybe you have not revised the weight paint, you go to youtube to find a tutorial about it, in fact I have just learn rig