Hello from Brisbane Australia

Welcome aboard.

Welcome. We have a charter member in Australia. Desmond.
Most likely your harmonicas are Richter tuned. On the low end there are 2 chords. A chord is a group of notes played together all at the same time. The blow chord is the same as the key of the harp. On a C harp the blow chord is C. The draw (inhale) chord is a 5th, called the V chord. Roman numerals. Folk songs often use three chords. I, IV, and V. 1, 4, and 5. Some simple songs just use I and V.
In C the I, IV, and V are C, F, and G. Just count cdefg, 12345. In G the chords are G, C, and D. GABCD, 12345. In the key of D the chords are D, G, and A.
These chords will not cover all situations, but will work with many simple folk tunes.
Solo folk harp is often played in the key of the harmonica. Use a C harp to play in C. This allows you to follow the melody using the notes in the middle of the harp and add chords from the low end.
When playing with a group it can often be advantageous to play in second position. That means using a C harp to play in G. Or a G harp to play in D. Your chords will probably harmonize more often in second position. In second position the I, or root chord is the draw chord.
For example, song is in G so chords are G,C, and D. Use a C harp and holes 1 through 4. Inhale for the G chord, exhale for the C chord, and fake the D chord by inhaling on hole 1 or 4 (which are both D notes).
Google some guitar chord shapes. Learn what a G and a C and a D look like. Then watch the guitar player's hand. Or get someone to write the chords above the words.
In second position you can play single melody notes that will most often sound correct, but there may be notes in the song that are missing on the harmonica. Bending can get you some more notes in second position but you aren't at that point yet. If you want to play the exact melody you probably need to learn it in first position now. That would be using a G harp to play a tune in G. The melody in first position will usually use holes 4 through 10.
When playing an instrumental tune first position is often a good choice. When backing up a song and playing little fills and harmony parts ad lib then second position often works better.

In first position play more blow notes and use draw notes less. In second position focus on the draw notes more.
Good luck. Be patient. It takes time. But if I can learn harmonica then anyone can!

Thanks so much for the replies. I don't have any formal musicalbackground but my children (all adults now) are always telling me to stop singing or whistling (in a nice way)...bit like you Keith..my music has just been for me up till now. I'll work through your advice Rex. A lot of my problem is confidence. It is a very informal group with about 4 fiddles, 3 accordians, 5 guitars a tin whistle, 2 other harmonicas and drum. They meet in a basement so lots of noise...I should be able to hide.
I will take on board your advice to listen more at first Rex.
Thanks again.
Roger.

That sounds nice. There are quite some different approaches on how to play the harmonica. I, for example, don’t like to play only single notes but prefer to have chords – but that’s purely a personal choice. The monthly songs here often showcase quite different approaches for the same tune. That did broaden my own horizon.

It’s advantageous that you have two other harmonica players in your group. I’m shure you can learn much by imitating & talking with them. It’s always easier to communicate face to face than by internet.

Shall do Rex...they only meet fortnightly so I'll record a song and post it next Monday.
Can I just say what a wonderful group this is...i'm still working my way around the site but it is proving to be so encouraging.
Thank you.