The Esplanade itself conducts guided tours. If you have at least 20 people, then you can get a group tour (they say you've to book it two weeks in advance, but there should be some leeway in that):
The tour is for a minimum pax of 20. Each Tour is about 45 minutes.
Tour would begin from the Concert Hall Information Counter and end at
the Esplanade Shop. Access into the performing venues, such as Concert
Hall and Theatre is subject to availability. During the tour,
participants will be briefed on the making of Esplanade and the
special features of the arts centre. Participants will be provided
with an information pack as a souvenir. The Esplanade Tour is priced
as follows: Adult: $8.00 inclusive of GST Children (aged 12 years old
& below): $5.00 inclusive of GST
(GST is Singapore's equivalent of VAT.)
If you have a smaller group or are travelling solo, then the self-guided tour is a better option:
Sign up for Esplanade iTour** if you prefer the freedom of exploring
the centre on your own. With the help of our Personal Digital
Assistant (PDA) linked to smart technology, you may navigate the
centre, hear fascinating anecdotes, view valuable footage and gain
insight into Esplanade’s workings. Booking the Tour : Tickets can be
purchased at the Concert Hall Information Counter. Available daily
from 10am to 6pm (including weekends and public holidays) Price : $10
per adult, $8 per child (7 – 12 years old)
** Including a sneak peek at the Concert Hall and Theatre, subject to venue availability. Please note that your Identification Card or
Passport is required for the loan of the PDA.
You'll find loads of other tours on sites like Viator or through travel agents. IMO though the best options would be either to take the self-guided tour or grab hold of a knowledgeable Singaporean! Go around sunset, that's when the Esplanade looks the most beautiful.
Personal recommendation: if you are in Singapore for a short while and are in the Esplanade area, go the Makansutra hawker stalls in the area. Sure, 'true connoisseurs' will turn up their nose but if you're pressed for time it's an excellent place to try out a variety of Singaporean cuisine.