Innovators Parts has no open signup. An admin or owner of your team invites you by email address, and that invitation is what lets you in.
Ask an admin to invite you from Organization → Invite a Member.
Two ways in, both fine:
Either way you land in your team's organization straight away. There is nothing to set up and no invitation to go and accept afterwards.
For many vendors that is enough — the name, SKU and price are filled in for you. Fill in anything that is missing, set the quantity, and save.
Your part joins that vendor's open order, or starts one if there isn't an open order for that vendor yet. Add parts from two vendors and you get two orders, one per checkout you will actually do.
When the order is ready, open it and click Order from vendor. Where the vendor supports it, your cart is built in one click; otherwise you get a list of links to work through in the same tab.
Once you have paid, open Shipping & payment details and record the tracking number, the shipping and tax, and how it was paid — a card, a Kit of Parts voucher, or a mix. Attach the receipt while you have it in front of you; finding it again in March is nobody's idea of fun.
Drag the order between board columns as it progresses — To order, then Ordered, then Arrived. The whole order moves together, because that is how the box actually turns up.
Admins and owners can bring everyone else in from Organization → Invite a Member. Choose Admin for people who should manage tags and members, or Member for everyone else.
Since signups are invitation-only, this is the only way to add someone — nobody can create an account on their own.