In general, the active voice, is a clause in which the subject does the verb.
Conversely, the passive voice, is a clause in which the object can be seen to be doing the verb. Essentially it is a way of moving around the emphasis of the sentence by changing the word order.
"The business is concerned about the trade war."
In particular, if we look at this sentence, it may be confusing upon first inspection. The verb is 'is', and it is being done by the business. Put another way, the concern is being felt by the business, not the trade war. Thus, the above clause is written in the active mood. There is, as far as I can see, no way to turn this clause into a natural sounding passive-voiced clause.
"The trade war is concerning to the business."
This clause is also in the active voice, as the trade war is doing the verb 'is' (to be). That is, the state of being (to be something) is being done by the trade war.
Often it is easier to spot when a clause is written in the passive or active voice, but when the verb 'to be' is employed, and the particular ways in which some sentences in English are constructed with 'to be', like above, which voice is being used can become less clear.
If you need further clarification, feel free to ask for it in the comments.