You are a little on detail, but let's say you read a line from the varchar2 that looks like:

CONNORMCDONALD

To add this to a record which is:

record MY_REC is
(  fname varchar2(20),
   lname varchar2(20)
)

it would look something like

declare
record MY_REC is
(  fname varchar2(20),
   lname varchar2(20)
)

l_rec my_rec;
begin
  l_rec.fname := substr(file_line,1,6);   -- CONNOR
  l_rec.lname := substr(file_line,7);     -- MCDONALD (rest of line
end;

Plenty of examples on this site of how to *parse* a single line into multiple fields (eg comma separated etc) if you need do that as well