To be honest it´s hard to get really (realistic) good sounding strings from the stock Logic library.
But using the A(ttack)D(ecay)S(ustainR(elease) in the exs24 combined with a decent reverb should give you something useable.
Compression is used to reduce or kill dynamics. Used on every instrument in modern pop. With strings in a maybe "classical" environment, I don´t know.
There are many presets, staccato-legato, but again, you can use the attack/ release, among others to shape your sound......To create f. ex. vibrato use the LFO......
Hmm. Logic is a great tool, but what do you want for $199? The string sounds are OK somewhere deep in the mix, but if you want them up front and realistic, they just aren't up to it.
There are many 3rd party libraries from companies that do nothing else. I use East West QL Symphonic Strings, and East West Hollywood Strings. There are others that are as good. They are expensive, and still require a lot of practice to get them right. Hollywood strings is about 300 gig!!! That's why they cost a lot and sound so good.
If it was easy, there would be no art in it, would there?
is it possible to make string textures different like staccato or legato or accents?
The Factory sounds from the Orchestral JamPack contain quite a few different articulations for the strings (and other instruments/sections). They can be loaded separately, or there are combined settings where the articulations can be switched using the Mod Wheel (CC1).
I'd suggest taking a look at the channel strip settings first (10 Orchestral). There are some slightly different Settings within JamPack Symphony Orchestra.
You might find that you'll want to investigate other mixing/processing options later, but for now it'll do as a start.
Other posts have commented that the Factory sounds are not great by modern standards. There are plenty of 3rd party sample libraries available (most use Native Instruments Kontakt... East West use their own 'Play" plugin). Whilst these sound generally very very good, there is a significant cost involved.
LA Scoring Strings, Cinematic Strings, East West/Quantum Leap, Cinesamples, Spitfire and others (but I hope your bank balance is good)
In addition to the non-Logic stuff mentioned above, an exceptional product is the Vienna Symphonic Library. Their new Dimension Strings are superb, and their Appasionata Strings are great.
Apart from that, in answer to your original question:
Experiment with subtractive EQ's (rather than boosting freequencies) to smooth the strings. Try using a realistic Hall reverb (there are lots in Logic) and light compression only if you need it. Gettings strings to sound great is a complex art and not easily answered in a short forum post.
Of course it also depends on what type of music you're creating...