Hey, I asked you first, lol. Yes, I mean the Holy Spirit. Is there another? Yes we have a personal spirit, but it's a given that our spirit does not lead us or teach us, or empower us.
Here's how I see it, right or wrong. Before we're saved, the Holy Spirit is there nudging us, drawing us towards God. When we're saved, the Holy Spirit steps it up a notch for us. He fills us, guides us, empowers us to overcome temptation like Willie T & Gary said. They are right.
The Holy Spirit also teaches us. This is not a conscious thing that happens, like speaking to us (but He could!) Scripture says the the Holy Spirit bears witness with our spirit, and this is what I think that's talking about. He teaches our spirit directly, Spirit to spirit, and we're not even conscious of it. Personally, I think that much of this takes place at night when we sleep. When we're sleeping, our conscious mind is (mostly) shut down and there are no thoughts or distractions or questions or anything. We're told to search the scriptures daily, and I think that after we read, that night the Spirit cometh and bears witness and teaches us reveals to us, the truth in what we have read or experienced.
Scripture also says that the Holy Spirit prays for us. Because we largely do not know what we should pray for anyway. The Spirit can also come upon us at certain times for an anointing to perform a specific task for God. This happened to me once, but I digress.
I think living for the Spirit is largely, yielding to the Spirit. Being constantly aware of and looking for His presence, especially at decision making time, when temptation comes our way. We back off for a moment and turn introspective, not to ourselves, but looking for divine guidance, focusing upon God and perhaps asking (even heart to heart)...what should I do Lord? and waiting for an answer. It may not come audibly, but will come.
Exercising the reality of the Spirits presence daily, moment by moment. Using your spiritual senses for this. (We have way more than 5 senses). The Lord wants us to look to Him for everything. This is what living in the Spirit or for the Spirit means to me. Turning to the Spirit for guidance instead of our intellect, instincts or feelings.