This depends SIGNIFICANTLY on what you mean by "making clothes". If you mean SDT, there's some good tutorials on the tutorial subforum - I personally like
this one because it goes through a lot of the basics. The downside is that it doesn't cover some of the tricker parts - notably handling the breasts, since they require tweening. I don't think any guides exist for that currently.
Any specific questions can also be fielded on the
SDT Discord Server - again, assuming you're actually asking about SDT. If you're looking for something else (i.e. creating outfits for a different game entirely), you'll probably want to find a more relevant subforum within the site and ask there.