When you need to categorize tasks or add keywords to them, you can use tags. First you add tags to the task form, then you can use filter above the tasks to find tasks with particular keyword (tag).
How to add tags to Bitrix24 tasks
Open new task form to create a new task (or open existing task for editing) & navigate to More section below the form, the Tags option is listed there among the available options, click on it to unroll:
Go to Tags section, click on Add and select one of the tags you've added before.
To add a new tag, enter a keyword and click Create.
How to filter tasks by tags
Once the tags have been added, you can filter your tasks by tags. First, click on Filter & Add field & select Tag field in order to add it to the filter:
All tasks with the selected tag will be shown under the filter after filter tag condition is applied: