Just complete the ESTA online. Make sure it is the proper US government site and not a third party agency. Theoretically you don't need to print out anything, but if you are like me it is nice to have something. You won't have to fill out any forms when you arrive for immigration, only customs forms. I filled out one of the old (still current for nationalities not covered under the ESTA) immigration forms in January and the agent told me he is sick of the airlines still giving them out to people who are admitted under an ESTA and threw it straight in the bin.