What category should I put the expense of buying a trailer for the business? It will be used for multiple years.

@jaco433776 

The trailer is a fixed asset.  Create a fixed asset category called 'ABC Trailer' or make a sub-category of another fixed asset category (perhaps equipment) to keep your balance sheet from getting too cluttered and assign that category to the purchase.  Your CPA/tax accountant can make the depreciation entries from there.