You may already find it, "Temp_3.c" on the same folder of "blinky.c" is the example that demonstrates temp.sensor, ADC and UART.
C:\SiLabs\MCU\Examples\C8051F12x\C\Temp_3.c
This example uses "printf()" but does not implement "putchar()". So, you should implement it modifying the example by yourself as usual.
C:\SiLabs\MCU\IDEfiles\C51\Lib\PUTCHAR.C

Try on-chip debugger function such as break point, step execution, watch, etc. on the IDE. The "help" menu on the IDE gives brief explanation of the debugger.

Another examples are found in "Applications" web page on SiLabs site. Following examples are suitable for the next step.
"AN122 Annotated 'C' examples for the 'F02x Family"
"AN106 Interfacing an External SRAM to the C8051Fxxx"
"AN113 Serial Communication with the SMBus"
"AN123 Using the DAC as a Function Generator"
"AN201 Writing to Flash from Firmware"

Most of these examples are written for 'F02x. So,
"AN131 Porting Considerations from F02x to ’F12x"
and "Config2" configuration wizard are your friend.

Also, I recommend you to look through
"AN101 Configuring the Port I/O Crossbar Decoder"
because the Crossbar is one of the difference from other '51, though Config2 does most of the work to set it.

The latest version of SiLabs IDE, Config2, Flash Programming utility, etc. are downloaded from "Software Downloads" page.

"MCU User Forum" is a good place to find many tips.

Tsuneo