There are a few ways to can select multiple assets at a time:
1) Click the check mark when hovering your mouse over the asset:
Hover your mouse over the asset to click the check mark.
Once multiple items selected, you can use the toolbar to interact with it: Delete, Move, Edit Tags or set them to Live & Expire.
2) Hold Shift while clicking a second tick box to select every asset between the two
This is the fastest way to select multiple assets quickly.
3) Change your preference to Single Click to select:
In your Personal Settings: https://app.optisigns.com/app/s/personal-profile
You can check "Single click to select assets" this will allow you to single click to select the asset instead of opening it. Double Click will open the asset in this case.