When someone needs to buy or hire something important, like a house, a car or an construction contractor, they will often ask different companies to tell them how much it will cost and what they will do. This is called a "call for bids".
It's like when you want to have a birthday party and you ask different cake bakers how much they will charge to make and deliver a cake, and what kind of decorations and flavors they offer. You want to make sure you find the best cake that fits your budget and tastes by gathering information from various bakers.
A "call for bids" is a way to make sure that the person who wants to buy or hire something gets the best deal and quality for their money. It also gives companies a fair chance to compete for the job by showing off their skills and experience. This way, everyone knows what they're getting into and the transaction is open, transparent and fair.