The in-game settings are accessible from the side menu (click the -icon on the upper left screen of your browser window to open the menu).
As a player, there are a couple of things you can configure.
When checked, this inverts the default snapping behaviour.
The default grid size is 50px, meaning that the distance between the centers of two adjacent grid cells equals 50px. Because players can be using different screens (e.g. a projector, a laptop, a 4k tv), this size might not be wanted. This setting allows players to modify, individually, the amount of pixels used to render a single grid cell.
You can configure which colours you desire for your ruler, the grid (lines) and the fog of war. The opacity slider for the FOW colour is non functional, the DM can adjust this to their personal preference in the DM settings.
Last, but not least, you can select another language by choosing one of the supported languages in the drop-down menu. Note that PlanarAlly is developed in english and, thus, in case a translation of something in the user-interface is missing, the english version of the string will be displayed.