As @Sandor Dosa comented. It is a light leak.

It is difficult to know where the leak happened.

• Prior for you to use the film (a faulty film from start)

• Your fault during mounting the film.

• Your camera has a leak.

• The film is jammed.

• You handling the film prior to send it to develop.

• The lab during the handling and process.

The bad news is, as you stated that you are new, there is a big chance you provoked the leak.

A new magazine should not be put into the camera or removed from it in bright sunlight. Do it in an interior, if you can in low light (it can be done in normal interior light tho) This is the time most likely the leak happened. After removing the magazine put it inside the original container. If the container is transparent, put that container in a dark container, like the original cardboard package.

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But if all the lost images are from the start of the magazine, let's say the first 15 photos, there is a chance the magazine was mishandled, for example, someone simply pulled a lot the film outside the container.

Next time ask for the ruined film too, this way you can somehow diagnose where the problem is.

Here is a diagram, that might help determine a possible scenario when a leak might happen: