Okay, as for where things line up. As was mentioned in the comments, the Manga skips over things that were in the books and pulls in side stories from later books...and the anime skips over things that were in the manga. But here are a few 'line-up' points. I'm going to leave out exact details of what happens in those respective points so as not to spoil anything, but you should be able to put things together from there.
As it stands, the anime is actually further along in the story than the manga...so as of posting this, if you don't want to spoil the manga, stop watching at Episode 18 (Season 2, Episode 6). So, here are where things line up.
Book 1 -- Anime Episodes 1-10 -- Manga Chapters 1-24
Book 2 -- Anime Episodes 11-17 -- Manga Chapters 25-46(ish)
Book 3 -- Anime Episodes 18-current (should end at Ep 24) -- Manga Chapters 47-Current
There are a total of 10 books out there. Books 1-5 are the "Main Story" and books 6-9 are side stories focusing on a single one of the girls that surround Itami. Book 6 focuses on Pina, 7 on Rory, 8 on Tuka, and 9 on Lelei. Books 1 through 9 occur in chronological order. Book 10 is a collection of side stories that occur at differing points throughout books 1-9. Book 10 included the story that occurs in the manga but not in the anime where...
Lelei falls ill on the way to Rondel; and Yao, Itami, and Rory end up battling undead and a minotaur to get the cure for her
Book 9 is intended to segue into a 'Season 2' series of books (not yet released) that will return the focus back to Itami to progress the main story.
Assuming you are talking about the true battle with the Fire Dragon...you are presently at the equivalent of Episode 17 (S2, ep5).