Auto fill data in adjacent cells

Hello, 

I am trying to automate filling in of data in a column based on the data in the adjacent column. Specifically, I have two columns in a sheet relating to Habitat code (column A [I.e g3c]) and Habitat name (Column B [i.e. [Other neutral grassland]) in a separate sheet (Sheet 2). I want the habitat name to auto fill based on the habitat code when entered in the column to the left for quickness instead of typing everything every time when in the field surveying. All functions I have seen have been either for numbers or are not working in my case. If there is a way I can auto fill data on my first sheet, that would be amazing and save time in the field. 

Many thanks!