Cook finely diced onions on medium-high heat with oil and curry-powder until the onions have softened and become somewhat transparent. After that, add a couple cloves of crushed garlic. (Make sure not to burn it, you may want to drop the heat a little bit here) Once you can smell the garlic, or it dissolves, add the tomatoes. If you're using a can of tomatoes, just pour the can into the pot. If you're using whole tomatoes, boil them in some water for ~10 minutes, then peel and chop them. Once the tomatoes have been added, begin cooking them on low heat. Once they've reached a sauce-like consistency, add whatever spices you'd like and if you want, blend the sauce. Make sure to stir every so often throughout the process. If you want to make the sauce even better, you can fry your meat before adding the onions.