When making statements in French, you always need the subject pronoun. "We read" is NOT "lisons." "We read" is "nous lisons." (Do not confuse this with Spanish and Italian, both of which do not necessarily need the subject pronoun with the verb.)
"Lisons" by itself is in the imperative mood. It's a command for us: "Let's read."
- Lisons cette note. = Let's read this note.
- Nous lisons cette note. = We read this note.
Thank you. I have enjoyed using Duolingo to refresh and extend my French knowledge from school days. My wife is French and I am trying to learn. However, as engaging as Duolingo is, without a structured approach to such rules etc. I am not going to learn it through using the app alone. As a result I have just signed up to Rosetta stone hoping that this missing structure is provided through their approach. ETA Unless there's some resource within Duolingo that I am not aware of?
In the web version, there are grammar "Tips and Notes" located within each skill. They're not exhaustive, but they're supposed to help learners manage each particular tree skill. In the end, most learners still supplement their Duolingo with outside resources as they see fit.
If I recall correctly, Rosetta Stone does not provide grammar lessons. Unless they have changed something recently. I haven't used Rosetta Stone in five years.
Because let's is imperative (meaning used to command or order). Let's is a contraction of let us. Let us read this note. It's an imperative sentence even though it sounds just like a suggestion and are waiting for compliance. Think of it this way: if you are walking over to your student who just tossed a note in class that you picked up and saying to him, "let's read this note" the two of you are going to read the note.