You do not need to have a Coupa account or access to the Coupa Supplier Portal (CSP) to take part in sourcing events. You can access an event directly from your sourcing event email invite.
See How do I participate in a sourcing event? for more info.
Your customer (buyer) can set up Coupa to require you to have an account and sign in to view sourcing events. In this case, you get an email the first time you are invited to an event. The email contains your username (your email) and a link to set up your password.
If you sign in and you have been invited to or responded to multiple events, you can see a table with all the events you have access to. When you click on an event link, you can see the event details for that event. Above the table, you can see the invitation of the most recent event that you have been invited to, .
If you are invited to another event, your new invite email doesn't include a password setup link.
Use the event link, also sent in your invite email, to access the event at any time.