Most of the time our best indicator for the status of the atmosphere is the presence or absence of clouds. There are many different types of clouds and this information is by no means complete. For the purpose of serving you best as a beginner paragliding pilot, there are some cloud types that you will see often - some are good signs for flying, others are not.
Cumulus
These clouds are a thermal pilot’s best friend - they almost always are accompanied by consistent lifting air, or as you will hear many times in your piloting career: a thermal.
Cumulus clouds technically are formed when a parcel of air laden with moisture, rises to the dew point. At the dew point, a cumulous cloud forms. If the thermal doesn’t rise as high as the dew point, no cloud forms. In essence, cumulous clouds mark the tops of thermals. Small cumulous clouds, that look like cotton balls, can be very friendly and indicate good lift. When the lift becomes stronger, the cloud may start to become taller than it is wide. These "Cumulus Congestus” clouds should be avoided at all costs. They resemble Marge Simpson's hairdo. The lift under them may be very strong and you may not be able to escape. Not only is flying in clouds illegal, but they may also be very turbulent inside, and you have no horizon reference. You should be aware of the risks of flying in thermic conditions before launching into a sky of cumulus clouds. Mountains can help generate Cumulus clouds by providing the source for rising air or thermals. This is why mountain weather tends to be less stable than flatland weather. If cumulous clouds are the only clouds in the sky by mid- to late afternoon, there probably isn't much risk of thunderstorms developing. When these clouds become taller than they are wide, they become cumulus congestus and the chance of thunderstorms rises greatly.
Cumulus Congestus
Watch these clouds carefully. They are the first stage of thunderstorm growth and can become dangerous in a matter of minutes. Thunderstorms are the most serious type of local weather. Since the sun's heat energy is a major factor in thunderstorm generation, thunderstorms typically occur in the spring and summer. Winter sunshine simply doesn't deliver enough warmth. For thunderstorms to develop, the air needs to be warm, moist, and unstable—typical Spring and Summer conditions. These white or gray clouds with flat bases are taller than they are wide. The earlier in the day that they appear, the greater the probability that they will develop into thunderstorms. Their growth can usually be seen with the naked eye, and the faster they grow the more likely they are to produce a thunderstorm. The air rising underneath them can be very strong and the risk of "cloud suck" rises.
Since the weather in the United States generally moves West to East, cumulous congestus clouds to your West are much more dangerous than cumulous congestus clouds to your East. This West to East airflow doesn't always hold true - especially in mountain ranges - so try to determine if the clouds are headed toward you so you can make a good decision on which way to fly to get as far away as possible.
Cumulonimbus
As the rising tops of a thunderstorm surge into the Jet Stream, the strong upper level winds drive the top of the cloud downwind forming the "anvil" shape of a cumulonimbus. At this stage a thunderstorm is capable of generating violent and unpredictable conditions including rain, hail, sleet, snow, lightning, flooding, gust fronts etc. If you see cumulonimbus clouds in the sky it is probably a good day to do something other than flying.
Lenticular
These clouds are smooth contact-lens shaped clouds. They are formed when very fast moving air is forced over a mountain or another air mass and typically form over mountain peaks or over the top of overgrown cumulus or cumulonimbus clouds. These are only formed when the winds aloft are very high.