What are some of the signs of dementia?

Please google the subject or use any search engine to explore. The question is way too general otherwise. If I were to give a few things to consider it is loss of short term memory and putting things in very odd places. You may mislay a lot of things, that being normal in aging. But if the keys are in the refrigerator and the butter in the car it is time to worry a bit. Can you give us some idea of your concerns?
Geaton has a good link for you to begin with as well, and there is other information of AgingCare. Go to the top and look under care topics for the subjects that interest you. May give you some fodder for more specific question for us.

Here is a good resource to answer your questions, including symptoms:

https://www.agingcare.com/topics/8/dementia-behaviors

https://www.alz.org/alzheimers-dementia/what-is-dementia