Sorry, but yes! This is a grammar lesson!

Homophones: pairs or groups of words that are pronounced the same, but have different meanings and are sometimes spelled differently. 

I know that to a lot of people this is absolutely and entirely useless knowledge, but it just so happens that I'm a total grammar geek (and an English teacher). So, in the spirit of sharing said knowledge with my students, I'm preparing and perfecting a class on homophones. They are a constant plague even for native English speakers, so it's understandable that for those learning English as a foreign language homophones are just another item to the never-ending list of things they hate about English because they make it that much more confusing.

These are just a few groups of homophones, in no particular order:

• There: a place or position
• They're: contraction of "they are"
• Their: possessive adjective; belonging to them

• Its: possessive adjective; belonging to it
• It's: contraction of "it is"

• Too: excessive quantity; as well
• Two: the number 2

• By: near to, beside
• Bye: goodbye
• Buy: purchase

• Four: the number 4
• For: in place of, 

• Write: to make symbols or letters on a surface
• Right: opposite of left; good or correct
• Rite: religious or solemn act

• Plane: airplane; level surface
• Plain: clear, evident; simple

What I do in this class is first pick a pair or group of homophones, explain the meaning of each word, and then write down a few example sentences where they have to figure out which word goes in which blank. I also like to separate them in pairs - Student A and Stduent B. SA tells SB a sentence using one of the words, and SB says which one is being used. I found some really great ideas on this website. If you have given these kinds of classes, I'd love to hear about what activities you use!

And down here, I have a special treat for those who read through the whole thing :)
This gallery illustrates in a more comical manner some other pairs of homophones.