To Add a Filter click the '+Add filter' button (1) on the left side.
Here you can choose which attribute to filter on (1) and set the condition (2). The type of conditions vary a bit between the different attribute types. In example numerical attributes has a greater than and lesser than condition and text attributes attributes has a contains condition.
If you can’t find the condition type you’re looking for, it is most likely because the attribute you have selected does not support that type of condition. In example you could accidentally be saving numerical values in a text attribute, which leads to the system not being able to apply a greater than or lesser than condition. To learn what types of conditions there are for every attribute type, see this article on Attribute Types.