You are about 10 generations of mining hardware too late to mine bitcoin with CPUs, mining pool or not.
2009: Bitcoin launched with CPU mining. I've been told that some people mined 50 or 100 bitcoins per day with an old laptop.
2010: GPU (graphics card) mining made CPU mining hard, so mining pools were invented. This way people could still mine with CPUs.
2011: GPUs had to get on mining pools, and CPUs were next to useless. Some hardcore CPU miners kept going but earned little. Gaming PCs made a good profit.
2011-2012: The first specialized bitcoin mining hardware based on FPGA chips. FPGAs gave GPUs a hard time. Some GPU miners kept going, but in 2012 earnings were slim.
2013: The earliest ASIC miners shipped to customers in january. ASIC mining completely destroyed CPUs, GPUs and FPGAs for mining.
Since 2013 there have been many generations of ASIC miners, each making the older ones obsolete.