How does a new left wing party spring up

Right wing parties I imagine are easier to create due to being able to get significant financial backing from businesses, but how would a for the people party even begin to gain traction?

Personally I would like to see a party focused primarily on the working class and middle class people, but actually tackling all issues around the housing, immigration (means tested for example to ensure people who need refuge are getting refuge and that the system isn't clogged) fairer pay for all etc etc. Too many details to dive into.