The levelling system (Battle Rank) gives no advantage what-so-ever, other than the requirement that you must be BR 10 or higher to be a squad leader. Therefore, given the same weapons and certifications, a BR 1 person will match a BR 20 person of the same skill level.
Of course, by BR 20 you are likely to have become a lot more skilled than you were at BR 1, and you're also likely to have earned and purchased a fair few certifications and maybe weapons. Note that none of the certifications are really an "instant win". For example, you cannot boost your health points beyond 25% above stock, and you cannot make a gun do more damage at all ranges, or buy a gun that doubles the damage done without any negative consequences.
A skilled player at BR 1 with no certifications and all stock weapons can still beat a player at BR 20 through skill alone, if he is particularly skilled.
However, this is not normally the case for new players. If you truly are new to the game and not ultra-skilled at FPSes in general, expect to die a lot and for it to be hard to get any kills. You really are learning a skill. If you get sick of dying, try out support roles like medic, engineer etc and stay behind friendlies for a while. Eventually if you persist you'll get better at combat though.