First, you need to choose the icon theme that you want to use. All of the available themes can be previewed at https://www.insanejournal.com/moodlist.bml . (Note: InsaneJournal does plan to include more mood icon themes in the near future) .
Now you can post using mood icons from both the Web Interface and from your downloaded client.
USING THE WEB INTERFACE:
In order to update from the website itself, click on the update journal option which usually can be found under the home category (Or you can go directly to https//www.insanejournal.com/update.bml or https://www.insanejournal.com/portal/) on all site schemes. From there you can select which mood to use under the event box.
USING A DOWNLOADED CLIENT:
Many clients available for download include the ability to add a mood icon to your journal entries. For more information about your preferred client, consult its documentation or its menu options. See https://www.insanejournal.com/support/faqbrowse.bml?faqid=129 for information on downloading a client. (Note: Not all LiveJournal clients are supported by InsaneJournal)