What is a bid or ask, what is an interest and how does origin and technology affect the trading and matching process
If you want to Buy certificates on GreenPowerHub you place a Bid.
A Bid is an interest, ie you have a buying interest in certain certificates, and when you place that interest it is active for the period you specify. When it is placed you need a seller with the correct certificates to place an Ask.
An Ask is a selling interest, i.e I want to sell certain certificates.
When all criteria between a Bid and an Ask are fulfilled it will create a trade. A trade is an agreement between a seller and a buyer that a seller delivers a certain amount of certificates, with certain criteria, at a certain time, for a certain price. For example this trade earlier today: 
is an agreement to trade 5GWh of certificates from one or more plants from the origin: AIB Hub grid-connected (see this article: Origins for details), at a price of 4.4EUR per MWh, i.e 22 000 EUR total.
The technology used in the plants needs to be Hydro, Solar or Wind, and it needs to be produced in 2023. Additional attributes and criteria can be set and would be respected before a trade would be made.
When a trade is done we will create a Trade confirmation for you and your counterpart to sign, and add it to your online books, see Trade process for details.
See the interest dialog for each market to see the available attributes relevant for that product group, here is an example of the current EECS interest dialog:
Origins
The origins play an important role in matching Buying(Bids) and Selling(Asks) interests.
See this article for more details