Arachne, Psionic Weaver

You must follow all normal timing rules when casting a spell with web-slinging. For creatures, that usually means you must cast it during a main phase of your turn while the stack is empty.

Card types other than creature include artifact, battle, enchantment, instant, kindred, planeswalker, and sorcery. Technically, you could also choose land, but lands are never cast, so doing so would have no effect. (The same is true for card types that don't appear in most games, like plane or scheme.)

The creature you return must be tapped at the time you pay costs, but doesn't necessarily need to be tapped before you start casting the spell. For example, if you tap a creature with a mana ability to pay part of the spell's web-slinging cost, you could also return that creature to your hand to pay the cost.