In the modern periodic table:
- elements are arranged in rows, called periods, in order of increasing atomic number
- elements with similar properties are placed in vertical columns, called groups
- elements in the same group have the same number of electrons in their outer shell (this is what gives them similar properties)
The table is called the periodic table because elements with similar properties occur at regular intervals.
Remember that the periodic table only lists elements, so you won't find compounds (eg water) or alloys, eg bronze listed there.