How To Play Up Bow and Down Bow
When we play the violin we either move the bow down towards the ground or up towards the sky. We have down bow, which looks like this symbol and means that you want to start with your bow at the frog, or the base of the bow, and pull your bow down towards the floor. Then we have up bow, which looks like this and means that you want to start at the point of the bow and push your bow up towards the sky.
If there are no bow marks noted, then you are typically going to start with a down bow and continue alternating down, up, down, up. The only exception to the rule is if you have a single note by itself before the start of the first full measure. This is called an up beat, and then you would want to start with an up bow. (These are usually marked, so you don't need to worry too much about it.)
In music, we have symbols showing both up bow and down bow.
Music will almost always start with a Down bow unless it is marked otherwise.