Start by picking a good chai tea. Since I don't drink tea from tea leaves, I use herbal and rooibos teas. I really, really love Teavana's Tulsi Dosha Chai Rooibos tea blend. It's so fabulous. (Photo from their website.)
A chai tea is a tea that is blended with cinnamon, cardamom, ginger, black pepper, and any combination of the above or other ingredients. It's warming and just a little spicey. You can make your own chai by starting with rooibos and adding the above warm spices.
Normally, you brew 1 1/2 tsp of rooibos for every 8oz cup of water. When you make a chai tea latte, you want to double the concentration because you will later double the volume with milk. I usually drink 16 oz at a time, so I would need 8 oz of brewed tea. That means I would brew 3 tsp of my tulsi dosha chai rooibos tea with 8 oz of boiling water. I add sugar during the breweing stage and I will use the same amount of sugar as I used tea, so 3 tsp of sugar in this case.
By the way, I love, love to use the Teavana Perfect TeaMaker even though I have a lovelier, prettier Bodum glass tea pot. To use the teamaker, add the loose tea, sugar, and then add the boiling water. Half of the pitcher is 8 oz. Fill to 1 cm of the top for 16oz. Let the tea steep according to the directions for your particular tea. When the tea is ready to pour, all you do is place the teamaker on top of your cup and a pressure mechanism opens to let the tea pour out the bottom of the teamaker, perfectly straining even the tiniest of rooibos leaves out of your tea. As soon as you lift the teamaker, the mechanism closes and the tea is contained within the teamaker. Easy peasy and no pouring or dripping, etc. For company, I use my teapot. For tea just for myself, I use the teamaker.
Here it is sitting over my teacup.

That little tea cup is an 8 oz cup. I prefer to drink tea out of my large, glass 13oz cup.
Continuing on, pour your steeped tea into your mug or glass. It should be only half full at this point. Next, take some milk and froth it with your preferred frother. I love this little $10 milk frother and I have to admit that I find it fascinating. Why haven't I known about frothed milk before?!!

To use this milk frother, pour milk in up to the fill line, which I think is only 2/3 cup, and pump up and down for about 20 seconds. Your milk will double, possibly triple, in volume and will be light and fluffy and so much fun! You can heat your milk before you froth it or you can froth it and then stick the (lidless) frother in the microwave for 20 seconds. Once you have warm milk froth, pour/spoon the froth into your mug until your desired volume is achieved. (I was going for 16 oz in this case.)
Seriously, look at the beautiful froth!

I love that it stays on top of the latte and can be scooped and swirled around without dissolving out.

So, to recap, for a 16 oz chai tea latte,
steep the following ingredients together:
- 3 tsp rooibos or herbal chai
- 3 tsp sweetener
- 8 oz boiling water
Once tea is steeped, pour into a mug. Froth warm or cold milk. If milk was cold, warm the froth in the microwave. Add 8 oz of milk/froth to the chai tea. You know have a delicious chai tea latte to enjoy!
On really hot days, you can make iced chai tea lattes. How exciting! Those are slightly more complicated as you have to make the tea even more concentrated since you will be diluting the tea with ice before you dilute with milk. I'm sure there will be a separate post on that in due time!