Very brief "how to get agent" guide by me who just got one. First off, you do need a 'manuscript' to pitch with, so if you're using your webtoon/webcomic you need to be upfront about this being for
print and that the digital rights are spoken for (if you are on contract). Make sure you share how beefy your reader base is. While they'll be a bit weird about the digital rights, knowing your audience size will likely swing them around.
Google search 'graphic novel literary agent' or get names of agents from the bios of creators you admire, many folks will list their agent. visit their twitter profile, read about the company and read about their query process. Each agency and agent is a little different. They use specific language to talk about what they're after, which you get used to after looking through a few websites.
Choose your agent(s) you want to query and prepare your query letter. The agency may have a guide, or you can usually follow something pretty similar to what you'd write for a synopsis.
If the agent is interested, they'll reply to request more information. At this point they'll be wanting something similar to what you might put in a pitch packet. Overview, character descriptions, synopsis, etc. Sample pages of up to 10 seem to be preferable too for graphic novels.
Repeat across multiple agents until one says yes. It's totally acceptable to have multiple queries out at the same time.
Agent contracts will be a 'from this project on' type deal, and some are 'opt in' while others are 'opt out'. 'opt in' is like you selectively bring the works you want representation with and they'll support you. 'opt out' is you are taken as being repped across everything, and can discuss opting some projects out of the arrangement.
Agent fees are typically between 12-15% per 'distributed rights' - so per deal. If they are a literary agent and you're wanting to move into audio/visual stuff they may bring on a second agent that will take another 5% for their role in negotiating you that deal.