Each man has a right to invest what he owns. 

He might chose to not consume his property, and also not to save it - rather, he might decide to try to use something he owns to produce something else which he will also own.

A man owns a field in which he plants wheat.  At the end of the harvest season he has twenty-five bushels of wheat.

He has a right to harvest the wheat, grind up some of the wheat for flour, to put some wheat aside for future decision-making, and to take the balance of his wheat and replant his field so that he can have another harvest later on.  This wheat is his capital.

This can only mean that:

Each man has a right to be a private capitalist. 

All that we have described here is the rightful (no permission is necessary) procedure whereby a man can support himself at his own expense to his own benefit.

Private capitalism simply means that a man may rightfully own productive property (a field, a plow, wheat) and employ it to produce more goods or more property.  That is what capitalism is all about.