Yes, you can use RAISE NOTICE like below. It’s correct the way you are doing.
RAISE NOTICE 'i want to print % and %', var1,var2;
See here for more information https://www.postgresql.org/docs/current/static/plpgsql-errors-and-messages.html
EDIT:
begin
INSERT INTO tbl1 (col1) values (val1);
raise notice 'insert tbl1 done!';
end;