this is a common question. Here's a tutorial that may help you:
Unfortunately, you cannot use mashier files with the HotPt module. The HotPot module does not understand Masher files. The HotPot module can only deliver single Hot Potatoes quizzes.
If you want to make a set of several Hot Potatoes quizzes and treat them as one single activity, I suggest you use the QuizPort module (for Moodle 1.x) or the TaskChain module (for Moodle 2.x).
Neither the QuizPort module nor the TaskChain module are part of the standard Moodle download, so you will need to install those module separately.
The QuizPort module is a mature and reliable module for Moodle 1.x. The TaskChain module is being developed, but a download link is not yet available.