What are the key roles of the House of Lords?

The House of Lords has 5 main roles: legislative, scrutiny, legitimating, deliberation and recriutment. However the first two are the most important. 

The legislative role is carried out through introduction of a Private Member's Bill such as Baroness Turner of Camden introducing the Easter Trading Act 2015; the PMBs are largely unsuccessful however as they do not recieve the necessary time or attention of the government. The House of Lords also had the ability to delay legislation for up to one year according to the Parliament Act 1949, this is particukarly important the year prior to a general election. 

In terms of scrutiny the House of Lords investigates and amends legislation at the 'ping-pong' stage of the passage of a Bill, as was the case for the Charities (Protection and Social Investment) Bill which which had amendments considered on the 22 February 2016 as proposed by Lord Bridges of Headley and Matthew Hancock. The Lords have the power to question ministers on a weekly basis and hold daily questions on government activities. Furthermore the House contains 6 select committees which allow the Lords to examine issues such as the EU and its role in preventing cyberattacks in its Member States. Finally, the Hosue of Lords can debate policy issues and draw the government's attention to its concerns, for example the HoL spent 8 days deliberating the AV Voting Bill to change the British voting system.