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It sounds like your husband stared a single member LLC, which IRS treats as a disregarded entity, meaning it is a part of the owner's tax return. With this, your jointly filed tax return will include a Schedule C for this business. Shortly, if the business makes profit, there will be self employment taxes applied to this profit. If the business has losses, then there will be no additional taxes.
This is all assuming your husband didn't elect this LLC to be treated as a corporation, doesn't have partners, etc.
Here is the IRS link that provides detailed info on the topic: LINK