Some people recommend HQM (Hardcore Quest Mod) packs as beginner packs, as they allow for a guided entry into mods. Unfortunately, many of these packs either alter the recipes to near nonrecognition or punisb players with outside challenges (limited water, more aggressive hunger, etc.). If you are just looking for the "Minecraft Theory" to learn the basics, then I'd say give one a go.
If, on the other hand, you want a more organic experience, drop Infinity out of Expert mode and play with the original recipies. Don't forget the powerful learning tool that is Creative Mode as well. I have a dedicated Creative Mode instance for any pack I play, just to test out block placement, mod interactivity, and general theorycrafting. This saves a ton of headache from wasting precious materials in crafting a bunch of machines/components that either don't work as expected or are simply not needed for the project at hand.
If you're not sure how something works, Google it. Most mods have a wiki in some state, and lacking that, someone else has likely asked about it somewhere. These forums are a decent place to come with questions as well. I hesitate to recommend YouTube, as far to many videos are either incomplete or grossly out of date, but sometimes you can strike gold with a decent Mod Spotlight. I can't stress enough, however, the importance of personal exploration and tinkering. There is no substitute for personal experience.