It is difficult to say what Shinto (神道) is because there is no such thing as Shinto, nothing in particular that the word refers to.
In the eighth century, the Chinese words "shen" (神, divine power) and "dao" (道, way) were used to represent the various folk practices that are commonly Japanese. This is also called kannagara (惟神).
In the Tokugawa era (1600-1868), some scholars began to study what they called kokugaku (国学), which can be roughly translated as "nativism," "Japanese Studies," or "Native Studies." One of their primary concerns was to valorize Shinto as a native tradition to replace imported traditions such as Buddhism.
From the Meiji era in the late 1800s until the abdication of the divine status of the emperor during the Allied Occupation, Shinto was defined as the national faith.
But Shinto has no single deity nor anything really resembling a deity. Kami do not create life, they are alive. They do not reward or punish people after death, people become kami. But then stones have kami or are kami. The wind is many different kami. Water is used in misogi ceremonies to purify one's understanding of the way of the kami but water is also kami.
Kami might be enshrined in a building (jinja) but the kami is not contained within or by the mirror or twisted paper at the centre of the shrine. The mirror and the shrine both simply make reference to the kami.
If Shinto is anything, it is how Japanese people, at least the elderly, behave towards each other and the natural world.