An observation is something we see, smell, feel, etc. That is, an observation is made by use of one or more of our senses. We observe something or someone all the time. An inference, on the other hand, is a possible explanation of the observation. For example, when we see someone yawning, we assume that the person may be sleepy. The first part, "seeing" someone doing "something" is an observation. The second part, the assumption that the person is sleepy, is an inference. The inference for any observation is based on our past experience and knowledge and can change if we make a contrary observation. Scientists make inference all the time, based on their experiments. We also make inferences for various observations in our day to day life. For example, if you see steam rising from a cup of tea, experience has taught you that the tea may be hot.
Hope this helps.