I would greatly appreciate your expert guidance. As an experienced runner with a slender build, I'm looking to develop muscle in my upper body. While I already focus on cardio, I want to add some mass to my chest, shoulders, and biceps, as my legs are already well-conditioned.

Where should I begin? 
What equipment should I invest in for home workouts, since I'm not comfortable going to the gym? Would dumbbells, a mat, and a bench suffice? 
Are there any helpful apps available that can assist in creating workout plans? (I have no prior knowledge of strength training.)

I welcome any advice you can offer for someone who is starting from scratch. Thank you so much! 🙏