Use "Hopefully..." to talk about something that you hope will happen. For example:

Hopefully we can finish the deal by the end of this month.

You "hope" for something that:

• might possibly happen
• isn't definitely going to happen

 So, for example, you can't say "Hopefully I can be a baseball player" if you're 30 years old and not athletic. It's too unrealistic. Instead, you would say:

I wish I could be a baseball player.