Click Manage
Model
(Model Explorer) in the Toolbar to display the Model Explorer.
Unlock any features that you wish to make selectable.
Click
to display the drop-down menu of Selection tools.
Click the selection mode to use.
Click an individual feature (left) to select it (right). Hold down the Ctrl key to make multiple selections.
This is the default selection mode.

Drag a window over a region of the model (left). Any selectable feature that is touching the edge of the window is selected (right).

Specify a box based on three points. Click to place the first point, then click to place a second point to define an edge. Finally, drag perpendicular to place the last point by double-clicking (left).
Only selectable features that are inside the box are selected (rright).

Specify an enclosed region based on three or more points. Click to place points and then double-click to place the last (left).
Any selectable feature that crosses the edge of the polygon is selected (right).

Specify the center point for a circular region. Click to place the center point, drag the cursor, and then double-click the desired radius (left).
Any selectable feature inside the region is selected (right).

Use the Expression Editor to select features or subsets using custom expressions you build.
Select all features that are visible in your current viewport.