I've personally met Gary Haugen, and know a number of people who work/have worked for IJM. Their main goal is to get laws passed in countries which do not have laws against slavery, and then to get those laws enforced. Often this involves using influence with first world countries to pressure these countries into applying their own laws.
Their other role is to bring (generally US) trained law enforcement to these countries to train local law enforcement to collect evidence, etc. They then use lawyers to pursue individual cases, and train local lawyers in their own laws so they can effectively prosecute slave owners. When they loose cases (which are always cut and dried) they investigate how the judge was bribed and take legal action. They will keep this up until they get all the way to the top.
My guess is that most of this money will go to getting law enforcement and lawyers on trips to India to do this. They will also use the money to change attitudes in the US, so that Congress can be coerced into doing the right thing (like adding anti-slavery clauses to trade agreements).