Hi! I see you are new.
To learn a language, click on "Home" and then "Basics1" and start doing the lessons. Hover over a word when you don't know it, and Duo will give you some hints and suggestions.
It's a good idea to read the Guidelines (there is a link at the bottom of every page) to see what is expected of us, behavior-wise. Empty posts like this that just say "Hi!" without any language related questions, tips, interesting articles, etc. are usually frowned upon because they take up space and don't add anything to the experience of other users here. But I figure as new as you are, you're just poking around and figuring out how everything works :)
This Unofficial "Getting Started" Guide is very helpful as well.