No one can answer how your computer will handle mods without first knowing the specs of your computer.
Just remember that upgrading a laptop isn't easy (if it's even possible) as Shadow Titan says, so be careful when you choose and make sure to buy one that can handle a game. There are gaming laptops that are fairly expensive - mine is not, it has a medium quality graphics card and good RAM and stuff, and I play on High with a decent amount of mods without any problems. I still prefer a laptop to a desktop computer since I want to be able to move around with it, take it with me when I travel and so on (I'm using it for other things besides gaming!).
To mod your game, you can either download mods from a site like Nexus or Steam Workshop, or you can make your own mods using the Creation Kit.. It isn't hard to make small mods and tweaks, but for bigger and complicated mods, you will have to have some knowledge about what you're doing.
As others have said playing on laptops can pose problems your better off making sure you can run it. One way is to post your specs, but another is to try http://www.systemrequirementslab.com/cyri, it checks your computer to see if you can run it. Gives a good starting point. If your just not sure.
Another thing to do to find out about modding is to find someone named Gopher on youtube. He's actually doing an modding for beginners series right now.