Do you need first months rent AND security deposit when you get a new apartment? Upfront?

My husband and I want to move.. we are viewing a few on Monday. But we will only have enough for either the security or the first months rent, not both. If we gave them the security would they hold the apartment for a month, then we could give them the rest of the money? Or how does that work??
Update: I don't mean me living there..I just mean them holding the apartment till I get the other half of the money
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