Alt-Ac stands for alternatives to academia. There are many other jobs other than academia that you can go into with a PhD.

The best way to find out how to apply a PhD to a non-academic career is to speak with people who are already doing it. Doing this earlier in your academic career is better - even if you're not certain that you'll be pursuing a non-academic job. Look for professional organizations in your field for people working in industry. Some of them have mentorship programs, which will match you with someone who is already working in industry. You can also ask people in your department to see which department graduates are working in industry.

You might discover that developing skill sets not directly related to your research might make you more successful on the non-academic job market. For example, if you do qualitative research, understanding quantitative research could help you expand the jobs you can apply to. Learning specific programs such as SPSS, R, GIS, etc. might also expand your job opportunities. Your university might have opportunities to learn these skills for free.

The fact that some people with PhDs in your field go on to careers where they use their skills doesn't mean it is an easy transition to make. It often requires a lot of hard work and luck.

To succeed in a non-academic job search you will have to learn how to translate your academic expertise into something which is valuable to a prospective employer. For some fields this is easy and obvious, while for others it will require a significant amount of work.