welcome to GoY.
most Echinacea are hardy so it could go straight in the ground. If it is big enough. Dig the soil where you want it so it is nice and lose. Put the plant into hole and back fill so the soil comes up to the junction between the roots and the place where the roots come from. Water well.

If the plant has fewer than 6 leaves then I would plant it up into a pot first in compost and then keep it watered until it has been in the pot for about a month. then plant it out.

Yes agree, get them in the ground as soon as possible. First soak the roots in a bucket of water for a couple hours so it's totally hydrated, then plant them. I planted my tiny seedlings last summer and they all survived the winter and are growing beautifully. They don't want a lot of fussing over - no fertilizer - not too much water either & they like lean gritty soil. They are true prairie plants.