In most cases where DHL, FedEX or UPS delivers, they may call you and ask your permission to pay any duties and taxes on you behalf. You will then have to refund them upon collection of your item.
You may also need to pay a one-time IDF fee of around KES 6,000.
If delivery is by Posta, you will received a card in your post mail that asks you to collect the package, in Nairobi, that maybe the Post Office at City Square. There you collect you package, move straight to custom desk, where an officer determines any duty or taxes you need to pay. if you have to pay, then you get sent off to the nearest National Bank. Pay your dues, take your package and go home.
But I am not sure if books attract duty and VAT. Computers do not.