I guess i may find some help here.

I am trying to plot a 4 discrete value i put in a vector as follows,
x = [ 4 2 4 1]
y = [ 2 0 4 1]
t = 1:4;

I would like to have a discrete plot with line connect each point. so I plot it twice.

plot(t,x,'o',t,x,'-')
plot(t,y,'*',t,y,'-')

Now I have problem creating legend for these plots. Does anyone know how to create a legend for this plots?

I actually want a tick on the x-axis to be something like ['John','Jame','Max','Dan'] instead of [1 2 3 4]
Right now, i know how to do it in the GUI, but don't know how to do it from the command. Need some help here too.

I found a solution,

plot(1:4,x,'-b<','linewidth',3)

Then legend will work

Yes. You can combine line style, marker and color like this. Regarding your second question you have simply to change the xticklabels using the function set. First be sure you don't have any other unwanted tick:
this will strip out any intermediate value, like 1.5, 2.5 and so on. Then you have to substitute the current labels with yours:
here I used a "cell array" (note the brackets) instead of a "character array", so I'm not forced to have strings of the same length and eventually include extra blank spaces. The above function accept "cell arrays" as well.
For any further detail, see