Hey! Sorry for getting back to you so late but to import images right click the asset browser and a menu button that says "import" will appear. I now see that this could be a little confusing and will push out a patch to make it more obvious.
For more information here is the wiki link: https://github.com/EarringPranksStudios/Tangent/wiki/Asset-Browser
Please get back to me and let me know if this works for you. Also, join the discord! I usually check there often.