Uncheck the "Select" checkbox if you want to always keep the current selection.
The two left-most text boxes show the current layer's position. You can directly type in values, or use the button on the right of each text box to open a slider.
At the center of the options bar are five alignment buttons.
At the end of the options bar is the parametric translation panel. The "X-", "X+", "Y-", "Y+" buttons move the currently selected layer exactly by the specified number of pixels.
You can also use the alignment panel and the parametric translation panel in combination to eg. place an object exactly 50 pixels from the right edge of the image.