Transmission has been possible ever since the LimeSDR was released. There are lots of modes and standards which can be used: FM, AM, SSB, simple digital voice with Codec2, amateur television (DVB-T2, S2 etc.), GSM, LTE and lots of others.
The easiest way to start is to learn GNU radio which has almost all of the components required for a medium complexity Tx/Rx project. I wrote a sinple GNU/Linux application (90% based on GNU radio) to demonstrate how easy it is now to do SDR thanks to existing open source chunks of code. You can look at the source code to understand how things are glued together, but if you want to do something by yourself, then you have to write your own code.
I would not recommend looking into software defined radio if you are not willing to learn aboutā¦ software
73,
Adi, YO8RZZ