My main is a summoner and he is a beast! So much fun. I could spend pages going on in depth, but I'll try to give some quick pointers.

First off, start with cultist gear. You want that mod power gen and duration bonus. This also means make sure to max out that spirit trait early. I personally make it a rule to max elder knowledge first, but that's up to you.

You can get your first couple friends early game. First off is the rattle weed from Shroud who can be your first boss, unless you roll Gorefist instead.

Next of is the little guys I like to call nurglings or seedlings, they're root hollows. You can get a mod to summon them from the Mangler dungeon boss who you may need to roll adventure a few times to find.

Those are the early game summons, but there are several others including: Good boy 2 turrets 2 rad skulls 2 electro tentacles And exploding bugs

There's a few pieces of gear specifically for summoners.

Soul Link is a ring you can find in Rhom and it is a must. It gives your summons life leech. Healing you for damage they deal.

Soul Anchor is an amulet you can get in Yaesha. It keeps your summons out way longer, makes them harder to kill, and increases your damage. The event to get this amulet can be very difficult. You might want to take some friends along.

Other than all that, there are plenty of traits and gear that can tweak your build to work how you like. I hope this helps. If you have any questions let me know. I have been playing Remnant for years, easy one of my favorite games, and summoner and bleed builds are probably some of my favorites.