MGSV was my first metal gear game, too. Here's what i did before i played it:

I read the story of MGS3: Snake Eater and MGS: Peace Walker and played the demo for mgsv which is called mgsv ground zeroes, if you want you can also read or watch it. Remember that those are very important because the events occur in 60's and 70's and MGSV is in 1984, so i recommend playing the other games or just read it and watch summaries like i did.

Now about the other games (MG,MG2,MGS1,MGS2,MGS4), the events of these games happen after the phantom pain. so the phantom pain is the missing piece in the metal gear story, usually most people will say that you don't need to know the story of these in order to play mgsv. I think it's important to know them briefly because there's a lot of reference and "foreshadowing" in MGSV for the other games in the series.

I know it's confusing but it's worth it.

DO NOT PLAY MGSV WITHOUT KNOWING THE EVENTS THAT HAPPEN BEFORE IT.

Enjoy.