I have an entry level DSLR ( Canon EOS 2000D). I would like to buy a lens for my camera to complement my current 18-55mm kit lens.
In particular, I am interested in landscape and portrait photography. However:
I believe a lens with better focal length can resolve these issues.
There is no "better focal length". Some focal lengths are good for some pictures, others are good for other pictures. About the only situation where "better focal length" might apply is if you have a zoom lens with a wide range of focal lengths. That might (or might not) be better than a narrower range. A narrow range on the other hand is easier to make sharp and have a wide aperture.
My heavy advice would be to buy a 50mm/1.8 "nifty fifty" first. It would be an ideal focal length for portraits, while at the same time blurring your background. Also for low-light photography it's great. It belongs to the 18-55mm focal length range you already have, so if you want to use it for landscape photography of objects far away, it doesn't help. But it solves the portrait background blur problem entirely.
For landscapes, if you want the ability to select your focal length from a longer range, an EF-S 18-135 zoom would give you extra range. But that's a far more expensive lens.
Some other considerations:
For many landscapes (as opposed to outdoor pictures of a single subject) a focal length in the 18-35 range is what you want. This gives a nice wide angle to "normal" view to capture everything you see. To take pictures of single objects that are far away you want a longer focal length. That reduces the angle of view and brings the object closer. For reasonable sized objects with your sensor people find focal lengths up to 150 or 200 mm useful. Wildlife, which is even smaller and further away, usually demands longer lenses than that. You can test what you want by taking a range of photos at the 55mm end of your existing lens. Crop them the way you want, ignoring the fact that they may be blurry from an extreme crop. Measure what fraction of the frame you are keeping along each axis. If you are keeping 1/3 of the frame you could get that angle with a lens of 3*55=165mm.
What you're looking for are probably two different lenses, particularly if your budget is limited. When selecting any lens, you need to consider the following factors:
... since the focal length of the kit lens is small, I couldn't take pictures of objects which are far away.
You could always get closer to your subjects. But what you probably want here is a telephoto lens (> 50mm focal length equivalence, and probably closer to 200mm or 300mm), probably a zoom. The typical budget recommendation here would be an EF-S 55-250 IS STM, but there are several options you can look at, depending on what you want to shoot and your budget. See:
In portrait photography, the background is not that blurry. I believe a lens with better focal length can resolve these issues.
There are actually multiple factors that come into play when it comes to getting a thinner depth of field and blurring a background:
Focal length might help, but might be counter-productive, forcing you to be farther away from your subject than you want to get enough background blur to make you happy. Max. aperture may be the easiest thing to purchase a lens for if you want to blur backgrounds. The most common recommendation here will be to get a fast prime (non zooming lens with a max aperture of f/2.8 or faster). An EF 50mm f/1.8 STM, but you could also consider the EF-S 24mm f/2.8 STM or one of the f/1.4 and faster lenses, which are more expensive.
Getting something like an EF 85mm f/1.8 USM or EF 100mm f/2 USM would probably get you even more background blur than a 50/1.8, but might be too narrow on a crop body to do more than headshots at a comfortable working distance.
