Enter the number of vocab words and grammar points you want in the 'Words' and 'Grammar Points' input boxes. Currently you can select between 1 and 10. After that, click on 'Select Vocab and Grammar', which will open the selection modal. Here, select at least one vocab list from the 'Vocab' tab. Next, switch to 'Grammar' tab and here click on any of the list to expand it. You need to select at least one sub-list / chapter in total. You can select that from any list, as well as select multiple across different lists. You can click and drag to select multiple instead of individually clicking each checkbox. Click on 'Close' or anywhere outside the modal to save the choices. There is also a 'Clear All' button which will clear all selected points from BOTH vocab and grammar.
After that you can click either Get Daily Selection or Get Random Selection as per what you want.
You can click on the words to open their Jisho page in new tab. The 'i' icon after words will show to which vocab set it belongs to. For grammar point, it will show the set and sub-point/ chapter it came from, as well as show the links for that point if present.
You can add custom sets to this, for which you need to upload a JSON file that has the data in a specific format. The format can be found Here. To upload the data click on the 'Add Custom Set' button, which will open the upload modal. Here, select the type, either 'Vocab Set' or 'Grammar Set'. Enter a title for the new set, which will be used in the selection modal after successful upload to indicate this set. NOTE that the title must be unique in its type (titles form vocab can be used in grammar and vice-versa). Add the JSON file, and click on upload. If there is any issue with the data format, the error will be shown, along with the word/point for which the error occurred. If everything was correct, the set will be added.
To download or delete a set, go to settings page.
Here are some resources which you can use with this, if you want to.
NOTE I'm not affiliated with any of these, and nor they related to this in any way (except jisho, see the explanation).
The words are taken from Jisho, where they are collected from JMdict, Kanjidic2, JMnedict and Radkfile dictionary files. These files are the property of the Electronic Dictionary Research and Development Group, and are used in conformance with the Group's license.
The JLPT tagging data comes from Jonathan Waller's JLPT Resources page.