There are English datasheets for all of the STC processors of which there are 10,11,12 and 15 series parts, IIRC. They have had two websites in the past, sometimes it can be a challenge to find what you're looking for.
Another starting resource is Github. There are many DIY digital led clocks sold with STC 15 series chipsets and there is replacement code for them on Github. Search there for STC DIY CLOCK and you'll find instructions for how to compile and download.
Downloading a program is similar to the Arduino process with several exceptions. Rather than issuing a reset to enter the bootloader code, you toggle VCC. Upon wake up, the processor waits for a certain time for a serial character to appear on a predefined com port. If it does, the bootloader process is invoked, otherwise it jumps to the user program. The other difference is that isolation diodes are required in the rx and tx lines of the serial adapter to prevent parasitic powering of the processor which would prevent the power cycle required to enter the bootloader. This requirement is well documented in the datasheets as previously mentioned.
The cp2102 serial adapter shown is suitable for download use but you'll want to keep the rx/tx/gnd wires short since they are 5v levels with cmos current. I have found adapter boards with cable jacks to be easier to deal with so I can use standard cables rather than the extension cable that would be required for the plug on the front of the cp2102 board.