Q:

How can I make a triangle with two rounded corners?

I need to create an image like this one.. It's a basically a triangle with 2 rounded corners.

A:

After reading your question again, I was answering a little more broadly with that last answer and assuming you would want to create more complex shapes in the future.
If you are really just wanting to create a triangle with two rounded corners, and you are using Illustrator CC, check this out:

create a triangle.

select the bottom left corner's anchor point with the direct selection tool then hold the shift key and also select the bottom right corner's anchor point.

see those fancy circles at the corners, they are magical. click on one and move them to the middle of your path to choose your desired corner radius.

And thats it.  Done!
It wasn't always this easy, Adobe added that with CC.  And sometimes you'll need to do things without a fancy tool like this, so I hope the pathfinder instructional was also useful.
Have fun learning Illustrator.  It is amazing!  Learning to use the pen tool will help you too.  But sometimes I just want to know that the angles and everything are right, so I prefer combining shapes to make compound paths, or using some of CC's new features like this one.

A:

Basic question, but we all started out learning too.  And im sure others can benefit from an instructional here.
To make a compound path in illustrator when your desired shape can be made of of two or more other shapes you use the pathfinder.  Your two shapes  are a triangle and a rounded-rectangle.
To access pathfinder select Widows >> Pathfinder
You now have a new window shown to you. 

Hover over those buttons to get an idea of what each one does. We will use two of these functions.
so to get started draw your first shape with the Rounded Rectangle tool.  If we just start drawing it will use the default of 10 pt Corner Radius and we need to change that.  So don't drag with it, click once with it in the area you want it, you'll input its dimensions manually. Chose the settings 
width: 150
height: 50
corner radius: 30

And hit Enter to see the first half of your shape done. Yay. 

Next the triangle.  You'll use the Star tool.  Again if you just start dragging it isn't setup right.  Click on anywhere on your artboard and change the settings to
Radius 1: 90
Raduos 2: 45
Points: 3

Then resize the resulting shape. With your Selection Tool to get the size triangle you need.

Now place it on top of your first shape.  The triangle is going to overlap the rounded rectangle, we are going to cut off its bottom points. The points at which they touch on the left and right should be just that, touching.  Not overlapping.  A view that helps with this is the outline view ( view >> outline )

Now select both paths and on your Pathfinder window use Divide (bottom left button)
This split everything up for you assuming all your paths were intersecting correctly.  Ungroup everything.  Select the bottom two corners with your Selection Tool

and delete them.

we are close.
last thing, select everything and use Unite (top left button) on your path finder.

if you got close with it but have some imperfections, you can take care of those with the smooth tool.
 the smooth tool is your it is your friend.
Now you know how to make compound paths! have fun with it!

