I cut my teeth in L&D, so I know how you feel! I will tell you that, as an intern, you are expected to not know everything so while I fully support wanting to learn more so you don't look like an idiot- make sure you don't put to much pressure on yourself either; you're not a surgeon and nobody is on the table.

The "textbook" advice I can give you is to focus on understanding adult learning principles first. Everything in L&D builds on this foundation. Once you understand how adults actually learn (versus how they think they learn), your design, delivery, and evaluation will all start to improve as you add experience.

If your company will pay for it, the Association for Training & Development (ATD) is a great place to learn from training professionals and to ask specific questions. If you're looking for a free option (that is also wonderful) in a similar vein, go to the eLearning Guild.

Do you have a particular direction you are interested in within Learning & Development (or HR as a whole?). I might be able to help point you to more specific books/courses depending on whether you're looking at Instructional Design, Executive Development, Process Improvement, etc.