If it's at the corner of the window, its orientation is diagonal and you can make the window larger, smaller, taller or shorter, or skinnier or fatter by moving the double arrow up, down, right, left, or diagonally. If the arrow changes to an hourglass, it means the OS is busy doing something that doesn't require action by you. You should wait until it changes back to an arrow before using the mouse again. If the arrow changes to a small circle with a diagonal line inside the circle, it means you are trying to drag something to a place it doesn't belong. Let go of the mouse button and start over.
Most mice have two buttons, left and right.
Some have three with the extra button being in the middle between the left and right button. Windows 95 recognizes which button you are clicking, whether it is a single or double click, and faithfully executes the action required by your clicks. A double left click chooses the object and initiates the action indicated by the object - to open a folder or load a program, for example. A single right click brings up a menu with a list of actions you can take by left clicking one of the actions on the list - copy to another location, for example. If, when you double left click, nothing happens on a more or less regular basis, Windows 95 may be interpreting the clicks as two single clicks because the click interval is too widely spaced.