To make space you can:
Delete texts or emails. If you really have lots, this can help considerably.
Delete or move photos, videos, documents, vetc.
Uninstall app updates.
Uninstall apps.
Clear cache files. However, this will only make space temporarily as cache files will rebuild over time. Also, while clearing cache files won't hurt anything, they're there to speed up operation and should be left alone.
If you can't move stuff to the SD card, move it to your computer or cloud storage.
Android since v1.0. Linux user since 2001.