All carts can be attached and detached by pressing R once while riding an entity with a cart nearby. This hotkey can be changed in the controls. Simply look for “Action Key”.
If the cart is going too fast, try toggling the slow mode by pressing sprint once while riding. This speed can be changed within the mods settings, but changing it will require a Minecraft restart to take effect.
If you want a certain non-vanilla entity to be able to pull the cart, add it to the list of entities in the mod settings. This is cart specific and you will have to find out the id of the entity to add it to the list. Adding minecraft:player will allow you to pull a cart without riding.