“Hold steady.”
Hold steady means to maintain your position without being shaken. In this investment conversation, the adviser means not to sell in panic after a sudden fall. The next sentence, Panic costs more than the drop itself., explains that character's reasoning.
“Patience and diversification — not putting all your money in one company.”
Diversification means spreading investments across multiple companies or products to reduce concentration risk. The verb is diversify. After the dash, the adviser restates it simply as not putting all your money in one company.
“Does that make sense so far?”
Does that make sense so far? checks understanding partway through an explanation. So far means up to this point. Replying in your own words, as Frank does with Spread it out, and don't sell in a panic., clearly demonstrates understanding.
“the patient ones outlast the clever ones.”
Outlast means to endure longer than someone or something. The prefix out- suggests exceeding another, as in outlive and outrun. Here the adviser says patient people remain longer than clever ones.
“That's the whole game.”
The whole game informally means the essence or central point of something. The adviser presents patience as what ultimately matters in investing.