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When we talk about substances and mixtures, we're looking at how different materials are organized. A **substance** is made of a single type of material with a uniform and definite composition. This means every part of the substance is the same as every other part. Common examples include pure water ( H_2O) and table salt ( NaCl) .
On the other hand, a **mixture** consists of two or more substances physically combined. They don't have a definite composition, and the components can often be separated by physical means. For instance, a salad is a mixture because you can usually pick out the different ingredients.
There are two main types of mixtures: homogeneous and heterogeneous. Each type varies based on how uniform the mixture is throughout.

A **homogeneous mixture** looks uniform throughout, meaning no matter where you sample it, it will have the same composition. This is because the substances are evenly distributed at the microscopic level. Solutions are a great example of homogeneous mixtures. When you dissolve sugar in water, it forms a solution that is equally sweet no matter where you drink from.
Red ink is another instance of a homogeneous mixture. All the color particles are uniformly mixed with the liquid, making it consistent in appearance and behavior throughout.
To sum up, if a mixture looks the same everywhere, it's likely homogeneous. This characteristic is why homogeneous mixtures are sometimes called "solutions."

A **heterogeneous mixture** is visibly different throughout. Unlike homogeneous mixtures, the components in a heterogeneous mixture are not evenly distributed, so you can usually see or feel the various parts. For example, oil and vinegar salad dressing is heterogeneous; you can see the two liquids separate after a while.
Consider the wooden beam. It is a heterogeneous mixture because its components, such as lignin and cellulose, are unevenly distributed. Likewise, freshly squeezed orange juice is another heterogeneous mixture. It contains pulp and particles that aren't uniform, meaning some gulps may have more pulp than others.
These mixtures exhibit diversity at the macroscopic level, making them easy to recognize because of their noticeable differences in texture or composition. If you can appreciate this mix of distinct parts without blending entirely, you are likely looking at a heterogeneous mixture.