Can someone explain the geography of HCMC?

One district has many wards. You should understand that ward is in district. For example, district 1 have 10 wards that are usually ordered like ward 1, ward 2 .... or ward Ben Nghe, ward Ben Thanh, etc. It's just the name of wards. Because range of the district is very big, so they are divided into wards. And it is not discriminated from ward to center city. The center of city is usually in district 1, ward Ben Nghe and other ward is near ward Ben Nghe in district 1. District and ward make an adress in the map.

Geographically speaking,the entire river districts and surrounds are former delta floodplains.
The highest point is 17M above mean sea level.
Houses don't sit on the ground,more like float on the mud.

You can Google a map in 1/10th of the time it took you to post. Why take someones word for something you can do yourself?

Anyway, here you go.
http://lmgtfy.com/?q=map+of+hcmc+vietnam+districts

The link from Adhome01 is good, I live in Sai Gon and the first image 'District map of Ho Chi Minh city is very useful. There are even more districts farther out that are not shown.
Some districts have numbers, probably all have names, at least two (5,7) are commonly referred to by both number and name.

It helps to know a little Vietnamese:
- Vietnamese for district is quan (ignoring the accent things - "diacritical marks")
- Vietnamese for ward is phuong.
- Vietnamese for street is duong.

I use Google maps on my iphone to find my way around and it is quite accurate. However, the geniuses at Google do not identify district names on their maps, only wards. If you zoom in, you will see 'PHUONG 4' for example. So, fairly useless unless you happen to know what district you are in.  (It is like a map of the US with just counties, and no states marked. There will be 25 Jefferson counties on it).

Apple maps does better, it notes the QUANs as well. Also, Apple shows more alleys if you zoom way in. (But my personal preference is google maps for readability.)