Run a PubMed search, and then on the results page select the items you need by checking boxes next to the citations; if you do not select any items, all the results up to 500 will be included in the list.
Under Send to menu click on Clipboard. You can conduct another search and keep adding your items to the Clipboard. The Clipboard can hold a maximum of 500 items. The Clipboard stores all the items you selected.
When the list is created, go to Clipboard. The resource list can be saved as a file, saved to MyNCBI Collections, printed, email, order by using Send to menu. Watch the Tutorial from PubMed MyNCBI