You will need to set regular meetups, most convenient if following a course that would have interested people come straight from class to the meetup. The location should be somewhere students can get to easily.
If you do have a class you can align with, ask the professor to allow you to do a 1minute promo at the start to ask people join you.
Write an email announcing the first meetup. Ask the department to send it out to students.
Get some sort of mailing list or groupware setup so people can join. If email lists, an "organizers" list and an "announcements" list.
Put up some posters with the date(s) of the meetups where your students are.
Announce your meetups 2-3 weeks in advance so people can schedule it in.
Try to do an event monthly to keep momentum. Skip December and some/all of the summer.
Ask people to suggest a talk in the advertisement.
Some meetups I've done are single-presenter, while others prefer the general conversation type of structure (5 minute talks, many people, etc). You will have to make a call on that until you have a few collaborators.
Ask for contributors/volunteers. You're going to want at least a president/spokesperson/announcer (probably you, for now), a vice president that knows all the rules and can step in as needed, and a person to take notes and manage bookkeeping when money gets involved. Three or more people involved make it easier to manage.
Your student union can probably get you beer money as a "student group", but you may need to invite professors to make it fundable by your university's rules.