Syntax: This is a compound-complex sentence structure. 'Oh yeah' is an interjection for emphasis. 'I'll tell you something' is a future simple tense clause introducing the main action. 'I think you'll understand' is an embedded clause acting as the object of 'tell'. 'When I'll say that something' is an adverbial clause of time (though note: in standard grammar, 'when' clauses often use present tense for future meaning; 'when I say' would be more common). 'I wanna hold your hand' is the main declarative clause stating the core desire.
Morphology: 'I'll' is a contraction of 'I will', showing future tense. 'You'll' is a contraction of 'you will'. 'Wanna' is a common informal contraction of 'want to'. 'Hold' is a base form (infinitive) verb following 'want to'. 'Your' is a second-person possessive adjective.

Syntax: Imperative mood is used with 'Oh please, say to me', which is a request or plea. This is followed by two noun clauses functioning as the direct object of 'say': 'You'll let me be your man' and 'You'll let me hold your hand'. The structure 'let me + base verb (be/hold)' expresses permission.
Morphology: 'Please' is an adverb used to make a polite request. 'Say' is the base form imperative verb. 'Let' is a verb that, when followed by an object and base verb, indicates permission. 'Your man' uses 'man' in the context of a boyfriend or romantic partner.

Syntax: 'And when I touch you' is an adverbial clause of time. 'I feel happy inside' is the main clause. 'It's such a feeling that my love' introduces a result clause, which is completed with 'I can't hide'. The repetition of 'I can't hide' uses anaphora for emphasis.
Morphology: 'Touch' is a present tense verb. 'Feel' is a sensory verb. 'Happy' is an adjective describing the subject's state. 'Inside' is an adverb modifying 'feel'. 'Such a' is a degree modifier used with a singular noun ('feeling'). 'Can't' is a contraction of 'cannot', showing inability. 'Hide' is a base form verb after the modal 'can'.