Sorry for the delay Warhammer newbies
Here is the next part of introducing Warhammer 40,000 armies.
The Imperial Guard
The Imperial Guard is the "regular," guy army in 40k. Many new players are drawn to this army because it looks normal to gamers, it's you and me in camo with guns.
Pray that you never get inducted in the Imperial Guard. The Imperial Guard is essentially every historical (and in some cases movie) army unit. What do I mean by that? The Guard doesn't have one uniform look. Do you want your guys to look like Laurence of Arabia then play Tallarn Imperial Guard. Do you prefer World War One Germans? Play Armaggeddon Steel Legion. Prefer a modern look to your army men? Play Cadian Shock Troopers. There are many more styles for me to list here. Looks are deceiving though as the Imperial Guard plays like the Red Army. If you play this army you will have waves and waves of cheap (and expendable) infantry, with tanks in support. You also have a few units that defy expectation in a futuristic army such as hobbits (called Ratlings in 40k parlance) and Ogryns (think ogres but not green).
The bottom line is the Imperial Guard are army men plus tanks and some goofy stuff
The tanks are not modern tanks but rather they are tanks more reminiscent of those from WW1 or WW2.
A word of warning for new players; you will lose A LOT of men in games! Don't get discouraged! You will lose 3 or 4 models for every one Space Marine.