You asked

How can I express and work?

If you want to keep breastfeeding your child, but you have to return to work, then expressing is the obvious answer. A portable electric or manual breast pump will be the easiest way to express at work, and you will also need to store the milk you have expressed to take it home.
Make sure that you take a cooler and a variety of storage containers with you to work in addition to your pump, and then store them in the fridge, or freeze them to take home with you. Breastmilk can be refrigerated for three to five days in the back of the fridge, where it is the coldest. It can also be frozen for between two weeks and six months. The former would be the case if you freeze it in a freezer compartment in a fridge, three months if your freezer section has a separate door, and six months in a chest freezer. Remember not to let frozen breast milk thaw if you are not going to use it within 24 hours (refrigerated) as it cannot be safely refrozen.
Once you get home, breastfeed as usual, and then send the refrigerated or frozen breast milk along with your child to his or her day care provider for use during the day.

More questions

Mums understand the benefits of breastfeeding and some may be tempted by online sources if they're reluctant to breastfeed themselves or are having problems.
Babies can often be fussy in the evenings and you may find it difficult to nurse or settle them. 
Here are ways to know if your baby is getting enough milk
Breastfeeding and medication: what you need to know
What's the difference between breastmilk and formula?
Breastmilk has plenty of iron to last your baby at least the first six months of his life. 
Nipple shields are used if baby wont take the breast or for sore nipples
As of February 21st 2011 the HSE is recommending that all babies, including babies that are breastfed be given 5 micrograms of vitamin D3 a day. This is because recent studies have shown that mothers and...
Spitting up is very common and most young babies spit up at least once a day. This is because their digestive systems are immature which makes it very easy for their stomach contents to come back up their...