Does my iPad 4th gen have a SIM card?

Only if you purchased a wi-fi + cellular iPad. Look at the back of the iPad towards the bottom where all the writing is. Just under the word iPad in bold letters, there is writing and it includes the Model Number. You should see Model A####. That is an A and 4-digits. Check this support document to find out if it is a wi-fi or a wi-fi + cellular. Identify your iPad model - Apple Support

If so, see this for where to find the SIM slot. Remove or switch the SIM card in your iPad - Apple Support

The cellular models of iPad 4g do have a sim slot you can put in a SIM card, the wifi only do not