Hello Mohd,
There are many different variations, but at the top level there are only three main types: Fixed price, cost plus, and time and materials. It might help if you focused on just those three to start.
These three main types cover the two extremes as well as one that is more mixed.
-At one extreme, you could agree to perform work for a set amount of money. No matter what happens (unless you have contractual escape clauses, but that's a whole different discussion), you are expected to complete the work for that amount. This would be a "fixed price" contract.
-At the other extreme, the buyer could agree to pay the seller whatever it costs to do the work, without specifying a specific amount. This would be a "cost reimburable" or "cost plus" contract. They are commonly called "cost plus" because in almost all cases the seller also gets some sort of additional fee or award, depending on the contract details.
-The mixed case would be "time and materials". In this case, the buyer and seller agree on a set cost rate for time spent on the project, and the seller agrees to pay any material costs. This combines some aspects of a fixed price (in this case, a fixed rate for the labor), and a cost reimburasble (for the materials).
After you fully understand these three, then you can dive into the specific varitaions -- like cost plus a plus incentive fee, or fixed price with economic price adjustment.
I hope this helps to clarify things!