Modded Minecraft naturally has a lot of differences from unmodded (vanilla). One of the first things you'll probably notice is changes to your inventory.
Different modpacks might have differences from each other, depending on the mods in them and the way they are configured. Most modpacks have these in common, though.
The item list on the right as well as everything highlighted in yellow is from Just Enough Items (JEI).
Everything in the top left corner is from FTB mods.
The minimap at the top right outside of your inventory is from JourneyMap.
Outside of your inventory, when you look at a block you can see at the top of the screen what that block is, as well as what mod adds it. This is added by the mod The One Probe.
It will also tell you what tool you need to break it, and what level of that tool you need. When it says "Pickaxe (level iron)" it does not mean it needs an Iron Pickaxe. It needs a Pickaxe that can mine Iron Ore.
It might also tell you other information about the block you're looking at, like what's in it and if it's doing something.