It’s easy to select lines in visual mode, delete them, then paste them a few lines lower. However, this won’t adjust the indentation to match surrounding code.

Instead, add the following to your vimrc (or init.vim):

" Move visual selection
vnoremap K :m '<-2<cr>gv=gv
vnoremap J :m '>+1<cr>gv=gv

Then select lines using visual mode (v or V) and press J or K to shift them down or up one line, respectively. This will also adjust the indentation properly (the same as pressing = while selecting the lines).