Click on the 2D symbol. Now enter..
Top box

2*x+y=3
Bottom box

x-y=5
Now after the horizontal bar enter..
x,y
For en exact key sequence...
[Click 2D symbol] 2*x+y=3 [DOWN ARROW] x-y=5 [LEFT ARROW] x,y
NOTE: If the cursor is in the column of equations you can click on the 2D key again to add a row and solve a system of 3 equations. You and add as many rows as you have equations.
Right now it only solves a linear system of equations. I've seen a request in this forum to have it solve non-linear equations, so who knows what will happen in the future.