There are direct flights to Inverness Airport from London (Heathrow, Gatwick & Luton), Amsterdam (Schiphol), Bristol, Manchester, Birmingham, Dublin, Belfast, Zurich … https://www.invernessairport.co.uk/fly-direct/
The airport in Inverness (like most airports) is a bit out of town. There are busses to get you from the airport to the city center and back. “The bus fares to and from Inverness Airport are around £3.10. Getting to by bus from the bus station to Inverness Airport takes around 30 minutes.” https://www.invernessairport.net/transport/buses.shtml
Or you can take the train from Edinburgh, Glasgow, London… (The TrainLine) . Click on map to enlarge.
Or there are buses from almost anywhere in Scotland. Here are some bus links:
I use google maps, put in the destination, then press the Directions button. Then you can add an Origin and select the thing that looks like a train.
If you’ve taken the ferry from Belfast to Cairnryan (Stena Line Ferry), then you can take the bus from Cairnryan to Ayr then the train to Inverness.