Generally, a tech deal begins when a larger nation sends you $3 million, usually for either 50 or 100 tech (that will have to be worked out between the two of you).
Once the aid package expires (ten days later), you buy tech until you're up to 50, and send it to your buyer as a foreign aid deal. If you're doing a 3m/100 deal, you'll need to wait another ten days to send the second offer of 50 tech.
Some forms (tech circles) have you send tech to a different person than you accepted $3 million from. In this case, you won't need to worry about the ten day waiting period.