How can I populate a custom form using Web Service

I am new to Web Service. I have a custom record form that I would like to populate using WS. Could anyone help me add information into a new custom record.

My Custom record has 3 fields
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Name  "My File Info"

Memo______________

File_______________
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I can populate the "Name" field with "My File Info" with the code below in C#. But I do not know how to populate the Memo field and File field.

CustomRecord nsMYinfo = new CustomRecord();           
RecordRef nsRecRef = new RecordRef();
nsRecRef.internalId = "43";  // Custom Record Internal ID
nsMYinfo.recType = nsRecRef;
nsMYinfo.name = "My File Info";
WriteResponse fileAttach = _service.add(nsMYinfo);