Interpretation of sample rate I'm a little confused about the sample rate:

If I have an audio file that was recorded with a sample rate of 48kHz, this means that there are 48,000 values per second in this file, right?

So when I read this file with a smaller sample rate of lets say 44.1 kHz I am summarizing every 44,100 values to one second so effectively I make the audio slower and thus longer than it actually is. Am I getting this correctly or do I have a total misunderstanding?
Yes that is correct-- if you sampled the audio recording at 48 KHz and then played those same samples back at 44.1 KHz you would be "time-stretching" the recording and it would be slower. However you can also resample the samples by the ratio of 147/160 to then have the 44.1KHz samples play back at the same speed.