What's a good point to start analog design with sky130? Is there a tutorial available?

https://www.youtube.com/user/bminch/videos This channel has lots of interesting videos about Xschem and Magic. Just try to install Open PDKs first.

Thank you. I'll explore the YouTube channel. I have already installed Open pdk. It looks like only digital cells are available in the library. Any idea where can I find the spice models of the MOSFETs?

If you have already installed Open PDKs, the schematic components are in /usr/share/pdk/sky130A/libs.ref/spi/sky130_fd_pr/ The schematic symbols for Xschem are in /usr/share/pdk/sky130A/libs.tech/xschem/ If you have already installed Xschem, there are lots of examples of circuits there ready for simulation.