There are two main ways to make your research Open Access: gold OA which usually involves payment of an article processing charge (APC) and green which involves depositing the output in an institutional repository (IR).
Gold OA means the full-text of the final published output (publishers’ PDF) is immediately available.
Green OA usually involves depositing a pre-publication version into the IR. This may be immediately available or it may be subject to a publishers’ embargo which can vary but is typically between 6-24 months. Funders such as RCUK and Hefce have laid down limits on these which can be found in the funders policies and mandates.