I want to buy 10 shares in X at $10 per share, you want to sell 10 shares in X at $10 per share, so I buy your 10 shares and now we have a...
...deal.
You have agreed terms, you have executed the trade, you have a (done) deal.
I cannot think of a general single-word term to describe making the agreements and doing the trade. However as a point of interest (hopefully), however in the insurance sector (UK) the term 'bind' refers to the moment the prospective Insured accepts the terms, promises to pay the money and therefore instates the insurance. From the moment the "risk" is "bound" the insured is covered. I don't think this word-use applies to any other transaction though.