The first time either start script is run, it will download and compile besu and teku. If you already have these elsewhere you can set either the BESU or TEKU env var to the actual executable to use for one or both of them (e.g. BESU=<besu-source-dir>/build/install/besu/bin/besu).

To start besu, run ./startBesu.sh

To start Teku, run ./startTeku.sh

The network is configured to start Altair from genesis and activate the merge at epoch 1. The execution layer begins as a Clique network and transitions to PoS at total difficulty 50. This means there is a reasonable period of time where the beacon chain has activated the merge fork but has yet to begin including execution payloads.