sign up and download a barcode.
print the barcode and take it along to your local parkrun at 09:00 on a Saturday morning and just join in.
At the end of the run you get given a token that corresponds to your position in the run and hand it in with your barcode.
They then publish your time on their results page and they send you a text and/or Email.
I think it's great and you can measure any improvement against your personal best.