You can do both the sugar and syrup or just one or neither. In fact, you could leave out the butter if you wanted but it does add a nice touch.
Preheat the oven to 350 or 400F, depending on what else you're cooking, if anything.
Cut the squash in half and scoop out the seeds.
Put about 1/4"of water in the bottom of a baking pan and lay the squash cut side down. Bake about 30 minutes, until softened. Take the pan out of the oven, turn the squash cut side up, add the butter, sugar and/or syrup, then put back in the oven for 10-15 minutes.