Before you push a transaction you first need to sign it. To do so you'll need to assemble your transaction object like so:
{
"code": "eosio.token",
"action": "transfer",
"args": {
"from": "fromaccount",
"to": "toaccount",
"quantity": "1.0000 EOS",
"memo": "memo"
}
}
Then call the abi_json_to_bin endpoint with the above payload which will return a json object like this:
{
"binargs": "0000000000ea305500000000487a2b9d102700000000000004454f53000000001163726561746564206279206e6f70726f6d"
}
With that you can construct your push_transaction object, it'll look something like this:
{
"compression": "none",
"transaction": {
"expiration": "2018-08-01T06:11:23",
"ref_block_num": 10855,
"ref_block_prefix": 473148127,
"max_net_usage_words": 0,
"max_cpu_usage_ms": 0,
"delay_sec": 0,
"context_free_actions": [],
"actions": [{
"account": "eosio.token",
"name": "transfer",
"authorization": [{
"actor": "fromaccount",
"permission": "active"
}],
"data": "0000000000ea305500000000487a2b9d102700000000000004454f53000000001163726561746564206279206e6f70726f6d"
}],
"transaction_extensions": [],
"signatures": null,
"context_free_data": []
},
"signatures": ["SIG_K1_JwLVG5pRdhvLfJGWkDEBPa7wdLbNeqeRFdvFrKDEryahSwCRpPb75m4auZh8frq6cXsm3dHit8GMbmuuBWxEjH"]
}
You can read more in-depth about it here.