Virgin to hair dye

So I have hair down to my waist, it's always been like a golden blonde color, but my roots are beginning to come in brown (my eyebrows are brown) and I've never dyed my hair before. I've been wanting to do it for some time now, just because I want to try something different but I'm nervouse I'll end up botching it 😶 I was wondering if anyone else has super long hair that they've dyed, how much dye does it take? Like I said, I'm new with this--any advice or tips welcome! Thanks in advance ladies!