What are these latches at the top and bottom of this window for?
In the second picture, the little thing that pops out (pointed at by the left-hand arrow) is a stop to prevent the window from opening more than about an inch. This way, when the window is open a little, nobody can open the window further from the outside to use it as a way of getting into your house. They can be a bit of a pain to latch down so the window can open further, if you desire to do so, but you push it flat, then slide it to the right and it should latch down, allowing the window to slide past it.
The two other items (pointed at by the arrow in the 1st pic and the right-hand arrow in the second) appear to be the locking mechanism that holds the window closed to prevent it from being opened at all. It appears that you pull down on the finger tab on the top one, and up on the tab on the bottom one, then slide the window open to the left. If these will latch into the open position, then you should be able to open each individually to leave the window unlocked, thus being able to open and close the window at will. They may, however, be spring loaded and require you to pull them both toward the center at the same time in order to open the window.
If these windows are several years old, there may be some of the general crud of life accumulated in them causing them to be a bit sticky and difficult to open. They may require a bit of force to open the catches, and possibly some cleaning.
In the pictures you've provided, it looks like the bottom catch is open, while the top catch is still latched shut.