"My mom booked a table."
订 in itself means to book
位 means a seat / seats
Many words in Chinese are formed in this way including a verb and a noun at the same time for elaboration. Often this kind of words can be used both as a verb and as a noun (a similar application as a gerund).
e.g. 骑马 Ride + Horse
However, it would be a little bit tricky to add adverbs and adjectives to such phrases and stay natural. Please acknowledge it first and move on.