Depends on your situation and what you want to achieve but one method could be to setup an ip address for vlan10 and another ip (and subnet) for vlan20.
Since both vlans now has route interfaces traffic will automatically be exchanged between the vlans if thats what you want?
That is (example):
vlan 10
vlan 20
int vlan 10
ip address 10.10.0.254 255.255.255.0
quit
int vlan 20
ip address 10.20.0.254 255.255.255.0
quit
int range gi 1/0/1 to gi 1/0/24
port access vlan 10
quit
int gi 1/0/2
port access vlan 20
quit
int gi 1/0/4
port access vlan 20
quit
Now, clients attached to vlan10 ports will set 10.10.0.254 as default gateway while clients attached to vlan20 ports (1/0/2 and 1/0/4) will set 10.20.0.254 as default gateway.
And now they should be able to reach each other (in this case the 5500 will act as a router).
Another solution could be that you have another switch connected to 1/0/2 and then I would suggest you to use tagged vlans, that is "port trunk" like so:
int gi 1/0/2
port link-type trunk
trunk permit vlan 10 20
quit
A third option would be that you want vlan10 untagged and vlan20 tagged on this interface.
Then the config should look like:
int gi 1/0/2
port link-type trunk
undo trunk permit vlan 1
trunk permit vlan 10 20
trunk pvid vlan 10
quit