I heard that because of global warming it is going to be really hot (or cold), and way sooner than expected - is that true?
Some places will get hotter and some places will get colder, and the average global temperature will go up.
The reason global warming is now almost exclusively being called "climate change" is that an average increase in temperature affects much more than just the temperature at a given place.
The 2015 Paris Climate Agreement set a goal to keep average global temperature increase under 2 degrees Celsius, though we're unlikely to stick to that target given current trends. 2 degrees doesn't seem like much, until you consider that 2 degrees average means some places could warm by 10 or 15 degrees while others could remain the same temperature or even cool off.
This upset to the temperature balance is most significant in cold places, where small temperature hikes can greatly disrupt proper snow and ice conditions, and hot places, where the heat can already reach dangerous levels.
Additional impacts of climate change include severe weather from warmer oceans and shifting wind patterns, increased wildfires from droughts, and reduction in usable farmland as temperate zones move to higher latitudes.
The earth's climate is a complex web of connection. Disrupting any part of it can have a huge number of unexpected consequences.
Yes and No.
The answer depends on who is doing the expecting, what timescales are involved, what index of global temperature is used, what adjustments are made to that index to compensate for observational bias, and, crucially, what the geographical and political location of the person doing the expecting are. On a timescale of centuries, there has been warming (about half a Celsius per century) as we come out of the Little Ice Age which followed the Medieval Warming Period, just like the Roman and Minoan Warming periods which were separated by slightly colder periods.
On a timescale of decades the rate of change is inevitably much higher. In particular there was a much greater rate of cooling between the 1960s and the 1970s, followed by warming between the 1980s and the 2000s. On a scale of tens of thousands of years there will inevitably be warming as we come out of the current ice age, enjoy a period of a few degrees warmer, and later on re-enter the next one.
Trying to predict whether it will get warmer or colder in the next few decades is almost impossible. Climate models currently are very poor at predictions and accurate raw data in bulk globally is hard to come by, especially before 1880.
Some people, such as Ottmar Edenhofer and Hans Joachim Schellnhuber and many people in California believe that humans can change the global climate on a decadic scale by enacting global taxation change and global wealth transfer and expect this to happen.