It doesn't mean impossible. It means that something is difficult or complicated to do. Here's an example---> A fisherman handed me a fishing pole to use at the lake. I told him that I wanted to catch a big fish. He said, "Catching a big fish is a little tricky, but I believe you can do it! < Here's another example--> I asked my friend Robert how hard it would be to clean all the viruses from my computer. He said it would be a little tricky so I should do a lot of research before I start.

It means difficult. Something that is tricky means something that you can be tricked into doing incorrectly or that is hard to achieve but can be achieved if you are careful.