When you deal with processors and components, you must get into details.

If you want to go simple, you could literally put white glue on an LCD to the 8051, but that wouldn't be practical, now would it? I didn't think so.

To begin, you need to do the easy parts. If you can write code for the 8051 that accesses ports, but you can't write code that accesses memory, then you might want to connect the components to the ports.

Each 8051 has a set of ports. Each port pin is labelled Px.y, where X is the actual port number, and Y is the bit number in that port. Y can be from 0 to 7, where 7 is the MSB. and Y can be anything from 0 to 3 (except some chips like the at89c2051 where Y is 1 or 3.)

As for the LCD, you need to determine whether you use a character or a graphic one. If it is character, there are zillions of documentation about them. The HD47780 chip on it controls most of its operation. Have you tried searching here?
You might be surprised at what this site has to offer.

For the keypad, you need to be more specific. If it is a bunch of buttons arranged in a matrix, then you are on your own, because connecting buttons to a circuit is a no-brainer operation.

As for the stepper motor, I haven't really used them, so I can't help you with them.

For the 8051, you need to make sure that code is being fed to it all the time, and you need a clock that keeps the 8051 running. In most cases, a crystal can be connected between pins X1 and X2.

If your 8051 reads code from external memory, then you need to make sure that the data inputs of an 8-bit latch (74xx373 or 74xx573) is connected to port 0, the ALE is connected to the latch enable pin (I think pin #11 on the 8-bit latch), and the outputs of the latch connected to address bits 0 - 7 of your code. Address bits 8 - 15 are to be connected to Ports 2.0 through Ports 2.7.

You should probably look at the tutorials on here, because they have a sample computer setup.