You've heard some wrong stuff. Drew and Lees info is correct.
DI = Direct injection = for converting guitar and bass signals to mic level and. Often referred to as Hi-Z, as Z stands for impedance in the maths of electronics, and high impedance is the main defining characteristic of a DI (along with usually converting unbalanced to balanced). Generally DIs plug into Mic preamps.
Load box or speaker sim = a device that provides a load, as a cab does, that converts the power amp signal to Line Level. Line level is different to mic level and guitar level. You plug these directly into line ins on audio interfaces.
Mic Preamp = coverts mic level to line level. Mics, like pickups, produce very low level signals, though the mic inputs are lower impedance than DIs and already balanced, as mics are balanced output.
You can record an amp straight out of the preamp (which is line level output) into a line in from an effect looop out, though you will still need IRs as you are now missing your power amp and cab. You will need to leave the power amp on, with a load attached (either a cab or a load box).
You can only record the power amp out with a load box. Power amp output will fry most things.
Your best option here is to get an interface with a decent pre or two, some line ins and a Hi-Z/DI input. That way you have a DI and mic pre right off the bat, you have line ins for your pod (edit: and preamp out from the FX send of your amp) and you can upgrade to a red eye or type 85 or whatever later.