This is a one-way walk along the South West Coast Path. There is a bus service between Porthcurno and Land’s End although it is not very frequent so you must plan your walk accordingly.
For bus services and timetable: (check out bus service 1/1A) https://www.transportforcornwall.co.uk/services/TFCN/1
My recommendation would be park at Porthcurno and take the bus to Land’s End and then return by foot. Alternatively you could stay on the bus as far as Sennen Cove and walk back from there.
or for the trek in reverse:
Land’s End to Porthcurno Walk
Route map: https://www.outdooractive.com/