Differential Equations

DSolve[{y'[x]==a y[x]+1,y[0]==0},y[x],x]

DSolve returns a list of rules for y[x] In order to use
 
the results you apply these rules to y[x]  by using the 
/. operator
First we assign the list of rules to a variable and use
this variable later on in the Plot utility.

result = % /. a->1

Plot[y[x] /. result, {x,0,3}]

Save the graphical output in the file "MyFirstPlot.eps"
Goto your unix shell and open the file by typing the
command "gv MyFirstPlot.eps"

Export["MyFirstPlot.eps",Plot[y[x] /. result, {x,0,3}]]