Right-click the track, select "Edit track information...", and select the Lyrics tab in the new dialog. Paste your lyrics into the text box, and click "Save".
Re lyrics sources, select the "Tools" main menu item, and select "Settings...". In the dialog box, select the "Lyrics" option (under "General". There you can see all of the lyrics providers available to Strawberry. Select as many as you like! Or maybe just try one at a time until you get the desired lyrics.
If none of the above helps, click on the "Search" icon (magnifying glass), top right-hand side of this forum, and enter "lyrics" - you'll get a list of queries forum members have re lyrics - maybe one of those will help you.