Coin Control Options
To reach the Coin Control options, go to SETTINGS -> OPTIONS (Solaris Core -> Preferences on Mac)
Click the check box to enable coin control. You may need to restart the wallet for this to have effect.
Under the Send tab, click Open Coin Control.
Select coins to send - select specific UTXO (outputs) by checking the boxes on the left and then click OK at the bottom
Locked/unlocked - a padlock beside the amount indicates the coins are locked (cannot be spent until unlocking)
Priority - this indicates the priority in which your wallet selects UTXO to spend if you do not select specific outputs