Packages (formerly known as block folders) are intended to wrap one or several blocks to make them reusable. E.g., if you have blocks for some operation and want to use them in a different workflow, you can make a package with these blocks instead of copy-pasting them.
There are two ways of making a package:
To make a package from a workflow editor, select blocks first. You can select a block by pressing shift and dragging the mouse to the blocks you want to select. Next, right-click and choose "Set as package".
To make a package from a package page, browse to the packages page, choose "New package" and enter the name and description of the package.
To edit a package, open the packages page and choose the package you want to edit. It is the same manner you edit a workflow. The difference is that a package doesn't have the table and global data.
If you set the package as a block, it will only be treated as a block in a workflow. Proceed to the settings tab when editing a package to enable this option.
Block Inputs & Outputs
Right-click on a block input/output of the package to define the inputs/outputs of the block. Then select to set it as the package block input or output.
You'll see the inputs/outputs of the package block when using it in a workflow.
When you connect a block to one of the package block inputs, GoLess will start to run from the block you set as the input in the package.