1.00 means one standard lot which equals 100 000 currency units. For example 1 lot of USD - 100 000 USD
Buying 1 lot of EUR/USD means that you buy 100 000 EUR for respective amount of USD (according to exchange rate).
Selling 0.05 lot of EUR/CHF means you exchange 5000 EUR to respective amount of CHF.
Hope its clear.
Cheers.