Your question is fairly general when you ask what they mean in magic, however indeed they have a very important symbolic meaning when it comes to the craft. We use symbols constantly in our mundane lives to communicate ideas. Writing systems (alphabets and words) are an obvious example of symbols used to convey meanings. Symbolism can be considered the use of symbols to represent concepts. The symbols used may be either literal or abstract representations. Some symbols are cross-cultural and appear throughout early history amongst many cultures. For instance one such symbol is the sun symbol, often presented as a cross or circle.
Symblos aren't only drawings and amulets or any other stuff like the pentagram. Symbolism is a very borad term and I'll tell you why.
For example people experience symbolism in their dreams. Dreams are rich in symbols and often their message is only understood when interpreted symbolically. Meditation and trancework are areas where symbols are often encountered. Symbols can appear spontaneously, or be used to enter a meditative state. Astral projection and shamanic journeying are journeys that are rich in symbolism, as they are essentially forms of conscious dreaming. The symbols (including people, animals, entities, gods and goddess, plants, and locations) encountered within trancework and meditation can be interacted with, and transmuted if desired. When you use symbols in visualization, and learn to transmute them into new forms, you are actually working with very meaningful magicform of magic.
So symbols aren't only drawings you see or any other shapes... However the pentagram is an important one and I believe it has been explained to you already.