Simple syrup is one of the most essential things for any bar. As the name suggests, it's very easy to make. The ratio, 1:1, in the name means that we use equal parts by weight of sugar and water. If you don't have a scale, or are in a hurry, equal parts by volume is a very good approximation.
Simple syrup needs to be kept in the refrigerator. 1:1 simple syrup should last about 3 weeks to a month, but if you notice any cloudiness in it or anything seems off, throw it out. It is one of the cheapest things you'll use for your bar so there's no point in taking a risk on it.
You can extend the shelf life by adding .5 oz of Vodka or Everclear for every 8 oz of water used. The addition of alcohol can easily double the shelf life of the syrup. You might not want to do this if you use simple syrup for non alcoholic drinks for people who don't consume alcohol or for children.