noun
Refers to a physical object that holds something up, or metaphorically to a person or thing that provides emotional, financial, or structural support.
棚が落ちないように支えを付けた。
I put a support on the shelf so it wouldn't fall.
彼女は家族の心の支えだ。
She is the emotional support of the family.
支え is the noun form (support/prop), while 支える is the transitive verb meaning 'to support' or 'to hold up'.
Derived from the verb 支える (ささえる, 'to support'). The noun form 支え is the continuative form (連用形) of the verb, used as a noun.