A good starting point is simply the cheapest fresh, non-expired ISO 400 color negative film you can find from major brands like Kodak or Fujifilm. You don’t need Portra 400 to learn the basics, and cheaper consumer films can still give very good results.

The bigger issue is technique, not film stock: no film will rescue poor exposure or weak composition. To learn efficiently, note your camera settings for each shot so you can compare them with your results later.

Also try to be selective rather than “burning a lot,” because processing and scanning often cost as much as or more than the film itself. If you find a scene you really care about, bracketing exposures can be worth it.

If you’re completely new to photography, it may be cheaper to learn exposure, framing, shutter speed, and depth of field with digital first, then move to film once you have the basics down. After that, trying several different film stocks is part of the fun, since each has its own look.