When I was first married, I was given many Indian cookbooks as wedding gifts and continued to receive them as Christmas presents, birthday presents, housewarming presents... Many of these cookbooks will try to tell you that certain substitutions can be made, and the recipe will be just as effective, and the food will be just as good.
These cookbooks lie.
Yes, you can try to make roti with half white and half wheat flour.
Sure, you can use those drab little brown lentils sold in every grocery store in America instead of whichever dal the recipe calls for.
Yeah, if you don't happen to have a spice on hand, you can omit it.
But I don't recommend it. No, no, no.
If you're going to cook Indian, find an Indian grocery store near you, and make friends with people who run it. It's very easy. If you are of the Indian persuasion, you will be immediately accepted and lauded for your embracing of Indian culture. If you are not Indian, you will be immediately accepted and lauded for your embracing of Indian culture, and you will also be regarded as something of a charming novelty. It's fun!
Either way, and I wish someone had sat me down and told me this ten years ago, there is no excuse for not procuring the proper ingredients. Your tastebuds will thank you.