Mendeley Reference Manager has a three-column structure interface. 

1. The left-hand side column (column 1) provides you filtering options such as 'All References', 'Recently Added', 'Recently Read'. 

2. The column in the middle (column 2) shows you the references that you imported to Mendeley Library from your research. 

3. The column on the right-hand side (column 3) displays the details (or metadata) of a reference that you selected from column 2. 

Please note:

• You can modify the metadata of each individual reference by selecting the particular field. For example, author field/year/title. Sometimes, Mendeley may not capture enough details for a reference and you will need to modify/add the details to ensure accuracy. 

4. The 'Add new' button

You can use the 'Add new' button to add references into your Mendeley library. You can add one file or multiple files into Mendeley library by selecting 'Import file(s) from computer'.

• You can also add a whole folder of PDFs into your Mendeley library. Alternatively, you can add a reference manually (for references that can't be imported automatically).