How to “Buy” index fund shares in Fidelity app?

Hey all,

I've done my research and want to put 100% of my rollover IRA funds into the Fidelity Target Date Index Fund FFIJX.

How exactly do I do this? Do I go to Transact > Buy > Enter the full amount of my IRA and then just “Buy” it?

Thank you! I'm very uninformed on this process…