Ticking sound under the hood and there is a milky substance on the oil cap?

Yep, it sounds like you have a blown head gasket but to be sure please check out the guides below. The engine ticking is normal when coolant is in the engine oil, do not run the engine anymore.

https://www.2carpros.com/articles/head-gasket-blown-test

If it comes back positive the cylinder heads will need to be removed so the gaskets can be replaced. Here are the instructions in the images below. You will need to drain the coolant and disconnect the battery before you begin. Check out the images (below). Let us know what happens and please upload pictures or videos of the problem so we can see what's going on.