If yours is a "first gen Macbook" (2006, 13-inch white), then you can't upgrade OS X past 10.6.8 (Snow Leopard)
(There are possibly hacks to go beyond Snow Leopard, but not natively)
So - if that's what you have, and you have the original Tiger (OS X 10.4.11), then you can update some, just not to any system near the latest.
If you haven't touched the software very much since it was new, you could download and install the last combined updater for Tiger from
here. Installing that updater CAN help as it checks to make sure that all system files affected by the updater are installed, and in the proper location.
Updating to Leopard (or even Snow Leopard) can help (but you would discover that Leopard is a slower experience compared to Tiger, but you get more options for other software that is a little more up to date than you can use on Tiger, and you can even replace the internal hard drive with an SSD. That would give you a noticeable improvement. Either system would be purchased, and Apple still does sell Snow Leopard for about $20
here.
How much RAM do you have installed? If you haven't ever upgraded, you may still have only 512MB installed. You can max that out to 2GB.
So, you have some options.