Hi Sagitarian,
I'm not sure of the timescale here - that is when your friend mentioned Mars squaring Saturn because over the last few days (and currently) Mars has actually been trine to Saturn.
Alternatively your friend may have done your chart and this is an aspect which you have natally (If you post your date, time and place of birth I will be able to tell you that).
However, none of the above really answers your query so I'll try and do that.
Firstly Mars represents action, aggression, assertion, drive, courage, fighting, combatitiveness. Its the drive that makes you get up and do something to assert yourself in the world.
Saturn represents limitation, restriction, authority, the father figure, fear, the need for security, order, structure, organisation.
Traditionally both these planets were regarded as malefic - they brought bad things. Mars is the Roman god of War (Incidentally the Greek equivalent is Ares, or Aries) so Mars could well mean having to fight and die in the Ancient world. Saturn was limit, restriction something that stopped you achieving or put obstacles in your path. If Saturn was against you then you had a hard time achieving things.
The Square aspect is one of 90 degrees (quarter of the zodiac circle) and it was looked on as creating tension and frustration - something new that you have to deal with.
Put these three together and Mars square Saturn suggests that you might have to fight for (or against) authority, that you might have to fight your way through obstacles, that forces will fight to prevent you succeeding. At a lower level that you might have a fear of fighting or acting or at an even lower level that you want to act but you are continually frustrated by obstacles.
The trine aspect I mentioned above is very different from the square, energy flows easily and you have a natural aptitude - in this case you may be able to control your agression and direct it so that it has maximum affect. You may be able to use it to overcome obstacles.
A more modern view of Saturn's role is that of a teacher - Saturn presents you with situations that are a challenge. You might not like them but you learn from them and through the learning process achieve maturity.
Hope this helps - post your details if you want more.
edited to say that I started this before Dave's post above - so sorry for some repetition.