If you know what a PO looks like, a quote looks almost exactly like that. It is actually designed to be turned into a PO upon approval. There is no fixed format, at least for B2B transactions. Just search the Net for "sample quote".
Once you send in the quote, it will need to get approved by the person authorized to approve purchases in the range to which your quote total falls. If your product is cheap by enterprise standards and they are buying just a few seats for a particular group, that person may be the manager of that group. If you are selling a 100,000 seat license, or if your quote total is $1M or more, you may have to wait until the CEO, CFO, etc. have the time (though I've heard there are companies where any purchase above $1,000 must be approved by at least a VP.)
Then the approved quote gets passed to the Purchase Dept., which will turn it into a Purchase Order and send to you. Before they can do that, they may have to ask you to fill a 2-3 page Vendor Questionnaire so as to get you onto the Approved Vendors List.
The PO is a binding obligation to pay you, so at this point you are supposed to deliver your product or service (but see below) and bill the customer, i.e. produce an invoice referencing their PO # (this is important - they must be able to track down their PO) and explaining how to pay you, and send back to them. They will hand it over to Accounts Payable, which will forget about it at least until the last day of the payment term, which can be 30, 45, or even 90 days after the invoice date.
Now comes the most annoying part - collecting a late payment. Every once in a while, a payment will be past due, not because they do not want to pay, but because something went wrong in the above process. E.g. your invoice does not match any record in their database because someone has made a mistype in the PO, or because they have two vendors with exactly the same name, based in different countries or states, etc. Eventually you will get the money, but it may take several months of calling different people and emails flowing back and forth.
The radical solution is to sell via a large corporate reseller. These resellers are the outsourced Purchase Departments of the industry giants that buy millions of licenses for thousands of software products. The benefit to the customer is that they have to deal with one or few suppliers instead of thousands. The benefit to you is also reduced complexity, plus you will get paid right away and it will be the reseller's problem to collect the payment from the customer.
The interesting aspect is that there is actually no need to give the reseller a (significant) discount. The customer will be happy to pay them more, because the overall cost of making a thousand purchases from one reseller is lower than buying direct from each of the thousand vendors.
Wow, scrolled down and could not believe I have typed an answer this long. Winding up.
If your prospect is a very large company, you may safely tell them to buy from their favorite reseller. The reseller will then track you down and proactively help you if you tell them you do not have much experience with all that stuff.