This is where the fun begins
Technology mods are probably the largest part of modded Minecraft.
Tech mods have to do with generating and using power to do things. Automatic mining and processing ores are common with tech mods.
Most tech mods use the same energy system, Forge Energy (FE). However, a lot of mods use their own fancy names for it, like Redstone Flux (RF) from Thermal Expansion, Crystal Flux (CF) from Actually Additions, etc. They're almost always compatible between each other except for some mods that have unique energy systems that only work with themselves, like IndustrialCraft 2 which uses Energy Units (EU).