Water jet just knocks them all off the plants (and hopefully washes them away), it's useful if you've got lots of them. For a soap spray, get a cheap spray bottle and some pure liquid soap (Dr Bronner's unscented is good). Don't use detergent, it's not the same thing. You just need one tablespoon of liquid soap in a quart of water, mix it up well, and spray on your plants until the leaves start to drip. Turn over leaves and make sure you get everywhere. You can add about half a tablespoon of cooking oil (or neem oil if you can find it) to make it stick a bit better.
That's the version for aphids, it suffocates the little buggers.
You can add stuff to help in different situations, like if you also have powdery mildew you can add a little vinegar, if you have caterpillars etc chewing your plants you can add ground-up peppers and garlic.