what do the numbers and letters mean ?
like bmw 325 ci 745 li or i
lexus ls 430 es 330
mercedes c230, s500

im not of a car guy but im guessing it to do with the power of the car?

Well for BMW the first number used to be number of doors, the second was something & the 3rd was the engine size.

The c is for coupe, x is for all-wheel drive, etc etc.

Now for BMW the first number is for body style 3 (compact) 5 (mid-size) 7 (full-size) & 6 is for sport (about the size of a 5).

M3 is a 3 series sports car, M5 & M6 same thing.

The second two numbers r engine size (30 is a 3 Liter engine).

The l is always for fuel injection. In Europe u r more likely to see td (turbo diesel).

They r all different model types which will have different engines.

BMW has the 3, 5, 6, 7 series & the next two numbers represent the engine size though not the exact liters.

Lexus had the IS, ES, GS, & LS in just their sedans. IS is the sport model, ES is the luxury, GS is the performance luxury, & LS is the top of the line.

Benz has the C, E, & S class for their sedans. Each one is more expensive, more options, & is bigger.

As the cars get bigger & more expensive u can assume the engines will also increase in size. The numbers for Lexus & Benz signify different engines and/or trim types that tend to change from year to year

the bms r to do with power, the first number refers to what model it 1,3,5,6,7 or 8 series the second & third r to do with engine size the higher the number the bigger the engine size or power, they're not always exact though ie e46 323 has a 2.5 litre engine, the e90 330 has a 3 litre engine & the 335 has the same engine but has twin turbos on it. the c refers to coupe & the l refers to petrol injection (d is diesel).
the mercs & lexus idont really know. just to clarify (scott L above) the first number has never been related to how many doors the car has as the 3 series never had a hatchback until the nineties, before that it was either a 2 door coupe or 4 door saloon/sedan. spot on about the x though

curently, the 3 in 328i would mean 3 liter. It is harder to distinguish between BMW engines nowadays. l means normal, no AWD. X l means AWD, Ci normally means a coupe or convertible of the 3 series.