I have recently bought DA:Inquisition, but I have never played any of the series. I have been told that there is some lore I should know beforehand to fully appreciate the story. What lore do I need to know before starting the game?
You should be familiar, at a minimum, with the events of Dragon Age: Origins and Dragon Age 2. There are also a number of tie-in items (books, comics, etc.) which you don't need to know. In my opinion, these games are both worth playing in their own right, but if you have to choose, DA:O is usually regarded as "better" (more fun, more coherent narrative), while DA2 is more closely related to the events of DA:I. DA:O plays more like a classic tactical RPG, while DA2 went for more of an Action RPG feel. Dragon Age: Awakening, a DLC for DA:O, is worth playing but not really required reading, and this is also the case with most or all of the DA2 DLC. If you do play both games, you can import your save from Dragon Age: Origins into Dragon Age 2.
Regardless of whether you play the first two games, you should play with the interactive movie in Dragon Age Keep. This will give you an extremely abbreviated plot summary of the first two games, prompt you for all of the major narrative choices in the first two games, and then present an interface (the "Tapestry") for editing another 300ish minor choices, including DLCs and other content you might have missed (the last part is entirely optional). You will then import all of these choices into your new Dragon Age: Inquisition save. This will allow you to ensure the game is in a consistent and "reasonable" state, and matches your headcanon. Unfortunately, I cannot guarantee that the interactive movie will be detailed enough for someone with no background in the Dragon Age setting, so you may want to look up various things in the wiki if you find yourself confused by anything.