1. simplest

:100,200 w filename

2. set a start mark named A first, set a end mark named B second, and then

      `: 'A,'B w filename`
1

3. set vim in visual model, such as ctrl+v, and then select all lines that you want to write to a new file, and then press shit+:

:'<,'> w filename # ‘<,’> will be filled by vim auotmatically

4. other

:+0,+99 w filename