The Metro Purchasers will place your order, track it, help return it, handle the invoicing. Your role is the following:
Get a Quote
This doesn't need to be a formal quote -- it can just be a printout of your Amazon cart -- but it will assist the Purchasers with knowing exactly what you want to buy. There's a tall tale of times past where 35 15" monitors were ordered. Because there was no part number or detail specified, UCD Purchasing (central purchasing folks) basically found the least expensive 15" monitors they could find. Computer lab wound up with 35 green monochrome monitors which, even in 1998, didn't fit the bill. So be informative with your request.
And of course, always ask the experts. That may be fellow researchers if you're looking for a new spectrometer and it will always be Metro IT (email@example.com) if you're looking for anything vaguely computerish.
Get an Account Number
Things cost money and there are very few who hold the purse strings. Faculty, the CAO, and a few people lucky enough to have their own grants or funding sources have authority to approve spending. If you're a graduate student, you'll need to request an account number from your PI (Principal Investigator, sponsoring faculty member) before submitting an order.
Submit the Purchasing Request
ETOX, WFCB, LAWR all use the PrePurchasing online purchase order system to submit requests. This lets you select your PI (if not you), vendor, be specific about your line items, add an account (or more if splitting between many accounts), attach documents (like a quote), and add any comments. You can then track progress of your order through the same system.
Once submitted, your order will route to your PI (if not you) for approval, then to an account manager to make certain the funds are spent according to the grant specifications, then onto the purchasers who contact the vendor (maybe by online form, maybe by phone, maybe by...egad...fax).