If you are using Autobid it will automatically buy parts of existing loans listed for sale by other investors that meet your return criteria. You can amend your criteria by changing your secondary offer rate within Advanced Autobid. Autobid will only purchase loan parts from other investors which do not have any mark-up applied by the selling investor.
If you want to choose individual loan parts to purchase, simply click go to the Loan Parts page of Lend on the Funding Circle website. Select the loan parts you want to purchase, and if you have sufficient available funds, click the buy now button.