If you open a demo or live account with an online Forex broker you have to use a trading platform in order to execute trades with that broker.
A trading platform is a software which provides a mechanism for the trade execution and includes additional tools to facilitate technical analysis like e.g. Japanese Candlestick charts with indicators.
Many brokers provide a choice of different trading platforms. Almost without exception every retail broker provides the Metatrader 5 platform. It is useful to have some knowledge about this platform and how it works. This video will provide an introduction to Metatrader 5.