Alright, time to share my biology knowledge with you 
DNA and RNA seem similar, but they have different purposes.
Let’s start with the basics of DNA:
DNA is the abbreviation for Deoxyribonucleic Acid. It is made out of sugar (S), phosphates (P), and Nitrogenous bases. The type of sugar it uses is Deoxyribose. The Nitrogenous bases are the important part because the way they are lined up makes the difference between different people (or animals, basically every creature). Those bases are Thymine (T), Cytosine (C), Adenine (A) and Guanine (G). Putting all of these parts together, one side of DNA can look like this:
S
|
P - A
|
S
|
P - C
and so on. Sugar and phosphates form a backbone for the DNA and the phosphates are tied to the bases. However, the DNA has another side as well, it is a double helix, two spirals that wind around each other. They are connected by their bases. Cytosine can only connect to Guanin and Adenin can only connect to Thymine. This would make our example of a structure look like this:
S . . . . . . .S
| . . . . . . . .|
P - A - T - P
| . . . . . . . .|
S . . . . . . .S
| . . . . . . . .|
P - C - G - P
In the end, it looks like this:
DNA is needed to store our genetic information in each of our cells. Our DNA defines, for example, whether we have blue, brown or green eyes. This information needs to be saved for long periods of time.
Now to the basics of RNA:
Basically, RNA is just the DNA cut in half. It only has one helix, so it’s just one spiral. Instead of Thymine, it has Uracil. The type of sugar it uses is Ribose. Other than that, it’s structure is similar to the structure of the DNA, for example:
S
|
P - U
|
S
|
P - C
In contrast to the DNA, there are different types of RNA (mRNA, tRNA, rRNA) with different purposes. In general, RNA is needed to produce the right proteins in the cells. It does not store genetic information but the information, what proteins are needed for the body.
This is all I can think of right now. If you have any more questions, feel free to ask! 
