# Documentation

### More details

In the following sections you can learn more about the key features of PennyLane:

![../\_images/code.png](https://pennylane.readthedocs.io/en/stable/_images/code.png)

1. [Quantum circuits](https://pennylane.readthedocs.io/en/stable/introduction/circuits.html) shows how PennyLane unifies and simplifies the process of programming quantum circuits with trainable parameters.
2. [Gradients and training](https://pennylane.readthedocs.io/en/stable/introduction/interfaces.html) introduces how PennyLane is used with different optimization libraries to optimize quantum circuits or hybrid computations.
3. [Quantum operations](https://pennylane.readthedocs.io/en/stable/introduction/operations.html) outlines the various quantum circuit building blocks provided in PennyLane.
4. [Measurements](https://pennylane.readthedocs.io/en/stable/introduction/measurements.html) presents the different options available to measure the output of quantum circuits.
5. [Templates](https://pennylane.readthedocs.io/en/stable/introduction/templates.html) gives an overview of different larger-scale composable layers for building quantum algorithms.
6. [Optimizers](https://pennylane.readthedocs.io/en/stable/introduction/optimizers.html) details the built-in tools for optimizing and training quantum computing and quantum machine learning circuits.
7. [Configuration](https://pennylane.readthedocs.io/en/stable/introduction/configuration.html) provides details about how to customize PennyLane and provide credentials for quantum hardware access.

## more developer focus ....

qml.state : <https://pennylane.readthedocs.io/en/stable/code/api/pennylane.state.html>

qml.kernels: <https://pennylane.readthedocs.io/en/stable/code/qml_kernels.html>

## Gradients and training ( @Variational circuits)

Step 1: <https://pennylane.readthedocs.io/en/stable/introduction/interfaces.html>

Step 2:<https://pennylane.readthedocs.io/en/stable/introduction/interfaces.html>

For Variational circuits: <https://pennylane.ai/qml/glossary/variational_circuit.html>


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