Just stab it with a fork a few times, put in a microwaveable dish, and cook for 10 minutes. After that, check to see if it is soft. Keep adding 5 minutes until the squash is done, there is no need to cut into it until it is soft (which will save the life of my fingers!)
But how do you eat spaghetti squash?
Use your fork to strip the squash into spaghetti (it will do it on its own when you dig into it). Then top with all the things you like on pasta. I love putting some olive oil, garlic, butter, salt, and mozzarella on it and eating it just like that. Try it out, it is a wonderful alternative to pasta.