Awesome! Tea looks the same throughout. You cannot see the different ingredients of tea separately. But, in the iron and sand mixture, you can clearly see the different ingredients. So, this mixture is not homogeneous.
If a mixture of two or more substances is uniform, the mixture is called a solution. For example, if you put sugar in a glass of water and stir it thoroughly, you get a solution of sweet water.
What if you used salt instead of sugar? Would you still get a solution?