Just to give you a brief overview.
Table is something that will have the real records (more than 1 record) in the database which gets created when we create a new document in SAP system or change a document or create master data or create transaction data or create a control data.
However,structure is somethin which is dynamically populated during various phases.Also the values in a structure gets refreshed once any operation is finished.Moreover it will have one record only unlike a table.
Table: Tabular array of data in the ABAP Dictionary. A table consists of columns (data values of the same type) and rows (data records). Each record can be identified uniquely by one or several fields.
Structure: A structure is a complex type and consists of components that can have any type (data element, structure, table type or reference type).
Structures are used in ABAP programs or to define the type of the interface parameters of function modules.