Definition: not closed or barred at the time, as a doorway by a door, a window by a sash, or a gateway by a gate; not shut or blocked.
There are many different ASL signs for the English word "open". This sign refers to more abstract concepts than physical-related concepts. E.g. "The store opens at 7am."
There are different signs for "open" as in "please open the door (or window) for me." "Open the book" and so on.
First 100 words.
As you feel more comfortable with the first few hundreds of ASL signs, progress further with your vocabulary and learn signing more.