To connect two JBL PartyBox 310 speakers together, follow these steps:
1. Power off both speakers.
. Locate the "Link" button on both speakers. It is usually located on the rear panel near the power input.
3. Power on the first speaker and press and hold the "Link" button for a few seconds until the pairing light starts to blink.
4. Power on the second speaker and press and hold the "Link" button as well until the pairing light starts blinking rapidly.
5. The two speakers will attempt to connect to each other automatically. Once connected, the pairing light on both speakers will stop blinking.
Now, the two JBL PartyBox 310 speakers are connected in stereo mode. You can control them using the controls on either speaker or via Bluetooth connection from a smartphone or other audio source.