How do I draw any conceptual diagrams of electrical engineering to make presentation and what is the best software that helps in drawing any type of conceptual diagram in any field of engineeering?

• Apache Open Office Drawing.
• Mathematia and geoGebra are great options.
• If you want a free, online  online conceptual diagram creator then you can visit -http://ian.umces.edu/symbols/.
• You could also try Inkscape, a free, open-source vector graphics software available from https://inkscape.org/en/.
• CorelDraw, Adobe illustrator, and PhotoShop,Sketch up are other examples.
• CmapTools, its free, the end result is super simple. Helps communicate the basic and helps organise ideas.
• MindJet - MindManager, it's nice, simple, you can attach files, and helps follow up tasks in the map.
• For special stuff, Adobe Ilustrator is great but it's not completely free - it's free only for 30 days but great for  infographics and diagrams where you need specific images.

Thanks for your help!