First, navigate to the "Syndicates" tab and then browse the list of available Syndicates. You can use the available filters and sorting options to narrow down the list.
Another way to find a Syndicate is to first pick your preferred pool and then navigate to Syndicates for that pool.
Click on a Syndicate to view the ticket selections. If you want to make a contribution, either pick one of the suggested amounts or type in your preferred amount in the free form box. You can join Syndicates from as little as 10p (or currency equivalent).
Once the ticket gets 100% funded, it is placed into the pool.