Most likely you already know that the topmost tool in the toolbar is the Selector and that clicking an object with that tool selects that object. Of course, there is much more to the Selector tool than that, but let’s look at this simple action in more detail.
First, note that clicking an object deselects any previous selection. Also, observe that with the Selector tool, you can not only select objects, but also drag the selected objects in any direction. Combined, these two features make it extremely easy and natural to move objects around, almost without thinking about “selection” at all: You see an object, and you click and drag it to where you want it. The click selects it, deselecting anything else, and the drag moves it.
Sometimes, this may be an annoyance. Especially if you use a tablet with a pen and not a mouse, you may find that it’s too easy to accidentally nudge an object when all you intended to do was just select it by clicking. To make this less of a problem, go to the Mouse tab of the Inkscape Preferences dialog and adjust the Click/drag threshold value. This sets the allowed “slippage” in screen pixels, the default being 4; if you click and drag an object by less than this many pixels, your action is still considered a click and the object does not move. Increase this value if you often end up accidentally moving objects instead of clicking them; conversely, decrease it if you find that objects annoyingly “stick” more than you like when you really want to move them.
Before you can click anything, however, you want to be sure that you’re clicking in the right place so that your click will not be wasted. Here, Inkscape is very helpful: It changes your mouse cursor when you are over a clickable area of an object, as opposed to an empty canvas where the cursor is an arrow. The exact shape of the over-the-object cursor is different on different platforms; for example, on Ubuntu Linux it looks like a hand, while on Windows it looks like a cross with arrows on the ends.
Play with this cursor-changing capability a little. You will discover that objects with no fill cannot be selected by clicking inside them and that fully transparent objects are not selectable by clicking at all (although you can select them with the rubber band, as you’ll see in the next section). In Outline mode (3.11 Rendering Modes), you can select any object only by clicking its outline.
As you can imagine, this changing cursor is less helpful in complex drawings where the entire canvas is often covered with objects. However, if you separate all the background objects into a layer and lock that layer (4.6 Layers), then these background objects, now unselectable, will stop changing the cursor—and you can again sense the foreground objects by moving your mouse over them.
Also, you will notice that every clickable object has an invisible margin, several pixels wide, on all sides. A click in that margin will still select that object. This is very handy for selecting small objects which would otherwise be almost impossible to accurately click upon. On the downside, this also explains why it’s sometimes so difficult to select the bottom object in a stack even if that bottom object protrudes a little from under the top one.
If you don’t like the size of this clickable margin, you can change it on the Mouse tab of the Inkscape Preferences dialog: Adjust the Grab sensitivity value, the default being 8 screen pixels. Note that both this value and the Click/drag threshold are in screen pixels. This means they do not depend on zoom, so even if the values remain the same, you will find it much easier to perform small moves and select small objects simply by zooming in.