On its own, the function =SEARCH(find_text,within_text) will return the position of find_text in the string that is within_text, and if not present, return an error.

so,

=SEARCH("rent","Current") will return 4, as "rent" is at the 4th character of "Current"

=SEARCH("rent","Sultana") will return #VALUE as "rent is not present in "Sultana"


=ISNUMBER(value) returns either true or false depending on whether or not value is a number, so,

=ISNUMBER(SEARCH("rent","Current")) will return TRUE
=ISNUMBER(SEARCH("rent","Sultana")) will return FALSE