13 The verb is a Hophal perfect with vav consecutive: וְהוּבָא (véhuva’, “and it will be brought”). The particle אֶת (’et) here introduces the subject of the passive verb (see a similar use in 21:28, “and its flesh will not be eaten”).
14 The construction is the infinitive construct with bet (ב) preposition: “in carrying it.” Here the meaning must be that the poles are not left in the rings, but only put into the rings when they carried it.

In other versions

And the poles shall be put through the rings, so that the poles are on the two sides of the altar when it is carried.

The poles are to be inserted into the rings so they will be on two sides of the altar when it is carried.

The poles are to be inserted into the rings so that the poles are on two sides of the altar when it is carried.

Insert the poles through the rings on the two sides of the altar.

And the poles will be put into the rings, and the poles will be on the two sides of the altar when carrying it.

And the staves shall be put into the rings, and the staves shall be upon the two sides of the altar, to bear it.

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