Hey welcome to webcomic-ing! For promotion there's a few ways it can happen.
The best is if the website that you're using to host your comic takes note of your comic and promotes it themselves. Anytime you hit the front page you're sure to see an influx in activity for the duration. Unfortunately this is mostly out of your control though, aside from just continuing to make the best content you can.
Another option is trying to put your comic out there through external means, like ads (paid or not) on various sites, trying to have people review or feature your comic, etc. This is a little trickier because you either have to pay out or try and find appropriate places to look at your stuff. For example, this is a cool youtube channel that focuses on checking out a wide variety of indie webcomics, and in the about section mentions how you can PM the owner to ask for your comic to be featured as well:
looking for opportunities like these have the potential to be useful
& Lastly, perhaps the most common method: self-advertising. Spending time both online and potentially in person to build up a name for yourself and spreading the word about your content. This is commonly seen by like engaging in social media and building a presence there. The results might take a long time, but it has the advantage that it's completely under your control. You live and die by your effort