I'm assuming you know how to run a text search so come back to me if this assumption is incorrect. Go to queries->Project(in the tool bar)->new query->text search.
Tick the "add to project" option in the top corner if you want to save your query as it's faster to change the word you are searching for than re-create the whole query for every search. Give your query a name if you are saving it – "Generic Text Search" for example.
Click on the text search criteria tab and type the word(s) or phrases you wish to search for. Change the all sources drop down menu under "Of" from all sources to selected items. Click on the now active "select" button beside it and browse for the sources you wish to narrow the search to (memos in this case).
In the "query options" tab select which output option you want (preview or create results a s new node as just two examples of such options).
Don't forget to spread your finds or you will just get the searched words coded to a node. For example, change the option from none to custom context and click on the now active "specify" window. Choose surrounding paragraph for example.
In this example, you have now searched your memos only for key words or phrases and coded the finds including their context to a new node. Your query is now ready to be re-used for further searches
Hope this helps but let me know if you need more clarity.