The component $X1$ is a crystal oscillator with a frequency of 16 MHz. In your project, this component is likely used to provide a stable clock signal to the microcontroller $U1$, which is the PIC16F877A.

Here's a bit more detail on how it typically functions:

In your schematic, X1 should be connected to the OSC1/CLKI ($U1:13$) and OSC2/CLKO ($U1:14$) pins of the microcontroller.

If you need help with how to connect X1 to U1, feel free to ask!

The component U2 in your project is an LT1932ES6#TRMPBF, which is a constant-current, step-up DC/DC converter designed to drive white LEDs. This integrated circuit is mainly used in applications such as backlighting for LCD displays. Here's a brief rundown of its key features and functionalities:

Pinout for the LT1932:

Let me know if you need more details on how to integrate it into your schematic!

The component $U3$ is an LM2596, which is a step-down (buck) switching regulator. It is used to convert a higher input voltage to a lower output voltage with high efficiency.

Here are the pin functions for the LM2596DSADJR4G:

The LM2596 is capable of delivering a fixed or adjustable output voltage and provides excellent line and load regulation. It is commonly used in applications where efficient voltage regulation is needed, such as in power supplies for microcontrollers and other digital circuits.