You can use a for loop to fill in the elements of a matrix. In your case, you are dealing with a 1 x 100 matrix, which is usually referred to as a vector.
It's often efficient to preallocate your matrix, that is, initialize its size:
in the above line, I create a variable m which is size 1 x 100 and each element is 0.
Now, I can loop through the contents and set the elements equal to the even values.
for i = 1:100
m(i) = 2*i;
The above loop runs for i = 1,2,3,...,100 and it sets the elements each time it runs through a value.
So when i = 1, m(i) = m(1) which is the first element of m, and then we set that element equal to 2*i which is 2*1 = 2. Then, i = 2, m(2) is second element, and we set that equal to 2*i = 2*2 = 4. You can see that this will continue until i = 100 and we set the 100th element of m, (m(100), to 2*i = 2*100 = 200.
You'll find that there are more efficient ways to create the matrix, such as
m = (2:2:200);
m = 2*(1:100);
but make sure you only use what you understand.
Hope this helps!