This may sound very obvious (and it is), but you need a valid passport.
You and every family member that will travel with you.
As explained previously, on the Express Entry process, you submit a form, wait for an invitation to apply (ITA), and only then you submit an application.
On the day you do submit an application, your passport must be valid for at least 6 months.
The whole Express Entry process takes a while, so consider renewing your passport so that you don't need to do it while the process is going.
If you do need to renew your passport while the process is going, it's ok, you just need to update your new passport information in your application.
You don't need to upload or send passports anywhere at this point, but their numbers will be needed when you fill the Express Entry Profile form.