How would I use the word "Salvation" as a noun in a simple sentence?
My first sentence was He gave salvation, but he is the noun in that sentence. My second sentence was Salvation was given.
You are mixing up noun and subject. In your first sentence, He is a pronoun and the subject. Salvation is a noun and the direct object of the verb gave.
If you need to use Salvation as the subject, your sentence is o.k.
You could also say,
Salvation is a key tenet of Christianity.
or
Salvation of the world's forests is important for the environment.